Free Business Tools & Calculators
Every free invoice24 tool in one place, built for United Kingdom businesses — invoicing, payroll, tax calculators, converters, PDF tools, and generators. All free, no sign-up required.
Invoicing & Documents
Invoice Generator →Create and send professional invoices, free, no sign-up required.Receipt Generator →Generate itemised, print-ready receipts for any sale or payment.Estimate Generator →Create a professional quote or estimate to send to a prospective client.Quote Generator →Create a firm, fixed-price quote or quotation a client can accept, then download as PDF.Credit Note Generator →Correct or cancel an already-issued invoice with a referenced credit note, then download as PDF.United Kingdom Purchase Order Generator →Create and send purchase orders to suppliers, tracked and print-ready.Expense Report Generator →Log business expenses and generate an expense report for reimbursement or accounting.Invoice Templates →Free, downloadable invoice templates in Word, Excel, and PDF.Estimate Template →Download a free estimate template for the UK with editable line items, validity dates, VAT notes, and Word or Excel formats.Quote Template →Download a free quote template for the UK with acceptance terms, expiry dates, VAT notes, and Word or Excel formats.Proforma Invoice Template →Download a free proforma invoice template for the UK with line items, customs/payment notes, VAT caution, and Word or Excel formats.Credit Note Template →Download a free credit note template for the UK with original invoice reference, reason, VAT adjustment, and Word or Excel formats.Delivery Note Template →Download a free delivery note template for the UK with delivery address, item quantities, carrier details, signature fields, and Word or Excel formats.Purchase Order Template →Download a free purchase order template for the UK with PO number, supplier details, delivery address, approval fields, and Word or Excel formats.Itemized Invoice Template →Download a free itemized invoice template for the UK with detailed line items, quantities, unit prices, VAT, totals, and Word or Excel formats.Receipt Template →Create professional receipts for your UK business. Add line items, calculate tax, and download as a clean PDF — free, no sign-up required.Document Templates →Fill-in legal and business document templates — free Word and PDF downloads, no sign-up.Invoice Templates by Industry →Download industry-specific invoice templates in Google Sheets, Google Docs, Excel, and Word.Invoice Generators by Industry →Invoice generators tailored field-by-field to your specific trade or profession.E-Signature →Sign documents electronically or collect signatures from clients online.
Payroll & Tax Calculators
VAT Calculator →Calculate the correct sales/VAT/GST tax to charge on an invoice.Salary Calculator →Calculate gross-to-net salary, tax, and deductions for an employee.Payslip Generator →Generate compliant, itemised payslips for employees each pay period.Hourly Paycheck Calculator →Calculate take-home pay from an hourly rate, overtime, and the full employer cost.Income Tax Calculator →Estimate personal income tax owed based on income and allowances.Corporation Tax Calculator →Calculate corporation/company tax owed on business profits.Two Jobs Tax Calculator →Estimate UK tax and National Insurance across two employments and compare entered tax codes.Pro Rata Salary Calculator →Calculate pro-rata salary from full-time pay, weekly hours and part-year work.Bradford Factor Calculator →Calculate an absence score from absence spells and total days absent.Holiday Entitlement Calculator →Calculate UK statutory holiday entitlement for regular, part-time and irregular-hours workers.Sick Pay Calculator →Calculate UK Statutory Sick Pay for 2026/27 from average weekly earnings and qualifying days.Maternity Pay Calculator →Estimate UK Statutory Maternity Pay for 2026/27 from average weekly earnings and weeks of leave.Taxable Benefits Calculator →Estimate employee benefit tax and employer Class 1A National Insurance on UK taxable benefits.Tax Calculator →Estimate UK income tax and National Insurance owed.Check a VAT Number →Verify a UK VAT registration number is valid.
Project & Time Tracking
Project Cost Calculator →Estimate total project cost from labour, materials, and overheads.Revenue Forecaster →Forecast future revenue based on historical growth and trends.Work Hours Calculator →Calculate total hours worked between a start and end time.Time Card Calculator →Total up weekly time card hours for payroll, including overtime.Timesheet Template →Log hours, breaks and overtime with automatic totals — no sign-up.
Business Calculators
Margin Calculator →Work out profit margin, markup, and selling price from cost and margin percentage.Percentage Calculator →Calculate percentages, percentage change, and percentage of a total instantly.Loan Calculator →Estimate monthly repayments, total interest, and amortisation for any loan.Investment Calculator →Project mutual fund and investment growth with compounding returns over time.Mortgage Calculator →Calculate mortgage repayments, interest, and amortisation schedules.Amortisation Schedule Calculator →See your full amortisation schedule, compare repayment methods, and model extra payments.Date Calculator →Add, subtract, or find the difference between dates in days, weeks, or months.Timber Calculator →Calculate timber volume, cut lists, log scaling, and firewood conversions.Flat Rate VAT Calculator →Work out flat-rate or simplified-scheme tax owed for small businesses.
Converters & Lookup Tools
Currency Converter →Convert between world currencies using live exchange rates.Unit Converter →Convert length, weight, volume, area, temperature, and more between units.Timezone Converter →Compare times across timezones and find overlapping working hours.Commodity Code Finder →Look up the correct tariff/commodity code for customs and import declarations.Sort Code Finder →Look up bank routing, sort, or SWIFT/IBAN codes for domestic and international transfers.
PDF Tools
Edit PDF →Add text, images, and annotations to any PDF directly in your browser.Watermark PDF →Add text or logo watermarks to PDF files in your browser, with no upload.Merge PDF →Combine multiple PDF files into a single document in seconds.Split PDF →Extract specific pages or split a PDF into multiple separate files.Compress PDF →Reduce PDF file size for easier sharing and emailing without losing quality.PDF to Word →Convert a PDF into an editable Word (.docx) document.PDF to Excel →Extract tables and data from a PDF into an editable Excel spreadsheet.Word to PDF →Convert a Word document into a shareable, print-ready PDF.JPG to PDF →Combine one or more JPG images into a single PDF file.PDF to JPG →Convert each page of a PDF into a high-quality JPG image.
Generators & Design Tools
QR Code Generator →Create a free QR code for a URL, Wi-Fi network, contact card, or plain text.Barcode Generator →Create free EAN, UPC, Code 128, GS1-128, QR, DataMatrix and print-ready barcode labels.Logo Maker →Design a professional logo for your business in minutes, no design skills needed.Logo templates for your business →Browse logo templates for 450+ UK trades and businesses. Edit on the page, download SVG and PNG free — no account, no watermark, no email.Letterhead templates for UK businesses →Create a professional letterhead in your browser – free, no sign-up. Sized to A4, address positioned for a DL window envelope; export as PDF or Word in seconds.Menu Maker →Design a restaurant menu free — scan your current one or start fresh.Menu Templates →Editable restaurant menu templates — fill in and download a print-ready PDF.Business Card Maker →Create and download print-ready business cards with your branding.Business Name Generator →Generate unique, available business name ideas for your new venture.SKU Generator →Generate consistent, structured SKU codes for your product inventory.Random Number Generator →Generate random numbers within a custom range for draws, samples, or testing.Password Generator →Create strong, random passwords with customisable length and character sets.Word Counter →Count words, characters, sentences, and estimated reading time instantly.Online whiteboard →Use a free online whiteboard in your browser. Draw, add notes, export your board and work without installing software.Remove Image Background →Automatically remove the background from any photo or product image.Image Resizer →Resize, compress and convert images in your browser — set exact pixels or a target size in KB, with no upload.Colour Picker →Pick any colour from an image and get instant HEX, RGB, HSL, HSV and CMYK codes.Email Signature Generator →Create a professional HTML email signature and copy it straight into Gmail or Outlook.QR Code Scanner →Scan a QR code from your camera, webcam, screenshot, or image.
Finance & Reporting
Conversions & geometry
Square Footage Calculator →Free square footage calculator for UK rooms, floors, and property listings. Enter length and width to get square footage instantly for flooring, paint, or estate agent listings.Square Metre Calculator →Free square metre calculator for UK rooms — square, rectangular, circular, or polygon. Get an instant m² figure for flooring, tiling, or paint quotes.Square Yards Calculator →Convert square metres or square feet to square yards — useful for US/Canadian carpet and turf orders. Enter your room size to get an instant square-yard conversion.Wall Square Metre Calculator →Calculate wall square metres for paint, wallpaper, or plasterboard — enter room dimensions and door/window openings for an accurate paintable area and cost estimate.Cubic Yard Calculator →Convert cubic yards to cubic metres for gravel, mulch, topsoil, or concrete ordered from US/Canadian sources. Choose your shape and enter dimensions for an instant volume.Square Feet to Cubic Yards Calculator →Convert square feet to cubic yards (and m² to m³) for concrete slabs, mulch, or gravel ordered from US sources. Enter area and depth to get the volume you need.Gallons Per Square Foot Calculator →Work out pool, tank, or raised-bed fill volume in litres or gallons per square foot/metre. Enter area (or length x width) and depth for an instant fill volume and cost.Elevation Grade Calculator →Free elevation grade calculator: enter rise and run to get slope grade percentage, ratio, and angle of elevation — for driveways, drainage, ramps, and site grading.Ramp Slope Calculator →Ramp slope and gradient calculator for wheelchair and accessibility ramps. Enter rise and choose a slope ratio (e.g. Part M guidance) to get the required run and ramp length.Mitre Angle Calculator →Mitre angle calculator for trim, coving, and framing corners. Enter the joint angle and board widths to get the exact mitre saw cut angle for each board.Angle Cut Calculator →Angle cut calculator for knee braces and diagonal supports. Enter plank thickness and the two leg distances to get the cutting angle and required plank length.Angle of Depression Calculator →Angle of depression calculator: enter vertical drop and horizontal distance to find the angle below horizontal for a line of sight — useful for surveying and site planning.Taper Calculator →Taper calculator for machining and woodworking: enter major diameter, minor diameter, and taper length to get the taper angle and taper ratio (e.g. 1:x).Rolling Offset Calculator →Rolling offset calculator for pipefitters: enter roll, set, and fitting angle to get the true offset, travel (cut length), and run for angled pipe around obstructions.
Concrete & masonry
Concrete Slab Calculator →Free UK concrete slab calculator: enter length, width and thickness in metres to get volume in m³, bag count or ready-mix order size and a real cost estimate.Concrete Column Calculator →UK concrete column calculator: work out concrete volume for round or square columns from diameter/side and height, with bag count and material cost.Concrete Cylinder Calculator →UK concrete cylinder calculator: for pours or standard QA test cylinders — enter diameter and height for volume in m³/litres, bags and material cost.Concrete Block Calculator →UK concrete block calculator: work out how many 440x215mm dense blocks and mortar bags you need for a wall, with joint-aware maths and a real cost estimate.Concrete Block Fill Calculator →UK reinforced-block core-fill calculator: work out how much grout concrete fills the hollow cores of a 440x215mm dense block wall, plus bags and cost. A niche technique in UK cavity-wall construction, mainly used for reinforced retaining/foundation blockwork.Cement Calculator →UK cement calculator: enter your wet (placed) volume in m³ and mix ratio to get cement, sand and aggregate quantities, 25kg bag count and material cost.Concrete Tube Formwork Calculator →UK concrete column formwork calculator (US "sonotube" equivalent): pick a tube diameter and enter height to get concrete volume, bags and material cost.Rebar Calculator →UK rebar calculator: enter slab size and T-bar spacing (BS 4449 T8-T25, grade B500B) to get bar count, total weight in kg and material cost.Brick Calculator →UK brick calculator: work out how many 215x102.5x65mm standard bricks you need for a wall, single or double skin, plus mortar quantities and real cost.Retaining Wall Calculator →UK retaining wall calculator: work out how many wall blocks you need plus gravel backfill volume and weight, with a real material cost estimate.Wall Volume & Cost Calculator →UK wall volume and cost calculator: enter wall length, height and thickness for a poured concrete wall, or block size for a masonry wall, to get volume and cost.
Aggregates & earthworks
Gravel Calculator →Work out how much gravel, MOT Type 1 or ballast you need by area and depth. Get volume, weight in tonnes and an instant cost estimate for your driveway or path.Sand Calculator →Work out how much sharp sand or soft building sand you need by area and depth. Get volume, weight in tonnes and an instant cost estimate.Crushed Stone Calculator →Calculate how much crushed stone or hardcore (MOT Type 1) you need for a driveway or sub-base. Instant volume, weight in tonnes and cost.River Rock Calculator →Calculate how much decorative river rock, cobbles or pebbles you need to cover a garden area. Get volume, weight in tonnes and cost.Limestone Calculator →Calculate how much crushed limestone you need for a path, driveway or sub-base. Get volume, weight in tonnes and an instant cost estimate.Asphalt Calculator →Calculate how much asphalt (tarmac) you need for a driveway or path, accounting for compaction. Get tonnage and an instant cost estimate.Jointing Sand Calculator →Calculate how much bedding sand and kiln-dried jointing sand you need for block paving. Get volume, weight and cost.French Drain Calculator →Plan a French drain (land drain) from trench dimensions: gravel backfill volume, perforated pipe run length and filter fabric area, plus cost.
Weights
Steel Weight Calculator →Calculate the weight of round bar, rebar, tube or rectangular steel stock from its dimensions and grade. Instant weight in kg and cost estimate.Steel Plate Weight Calculator →Calculate the weight of a rectangular, circular or ring steel plate from its dimensions and grade. Instant weight in kg and cost estimate.Aluminium Weight Calculator →Calculate the weight of aluminium sheet, plate, round bar or tube by alloy. Instant weight in kg and cost estimate.Metal Weight Calculator →Calculate the weight of bar, tube, plate or box stock in steel, aluminium, brass, copper and more. Instant weight in kg and cost estimate.Glass Weight Calculator →Calculate the weight of a glass sheet, panel or rod by shape, thickness and glass type. Instant weight in kg and cost estimate.Pipe Weight Calculator →Calculate pipe or tube weight from outer diameter, wall thickness (or bore) and length. Instant weight in kg and cost estimate.Timber Weight Calculator →Calculate the weight of dimensional timber (CLS, sawn or PSE) from length, width, thickness and species, adjusted for moisture state. Instant weight in kg.Log Weight Calculator →Calculate the weight of a tapered round log from its diameters, length and species, adjusted for green, air-dried or kiln-dried moisture. Weight in kg.Concrete Weight Calculator →Calculate the weight of a concrete pour from its volume or dimensions, by concrete type. Instant weight in kg/tonnes and cost estimate.Size to Weight Calculator (Rectangular Cuboid) →Calculate the weight of any rectangular box or cuboid from its length, width and height, using a built-in materials density table or your own value.
Carpentry & framing
Stud Wall Calculator →Calculate the number of timber studs, plates, and corner studs for a stud partition wall. UK "4x2" (100x50mm nominal) timber, 400mm/600mm centres.Rafter Length Calculator →Calculate rafter length from rise, run, and overhang, plus rafter count for your roof.Roof Truss Calculator →Calculate rafter/top-chord length and truss count for your roof, with material and installation cost.Stair Calculator →Calculate step count, riser height, tread depth, and stringer length for your staircase, checked against Approved Document K guidance.Spiral Staircase Calculator →Calculate step count, tread angle, handrail length, and headroom clearance for a spiral staircase.Spindle Spacing Calculator →Calculate spindle (baluster) count and spacing for a deck or stair railing, checked against a 100mm maximum gap convention.Wood Beam Span Calculator →Check a timber beam span against deflection, bending, and shear limits per Eurocode 5 (EN 1995) and the UK National Annex.Floor Joist Calculator →Calculate floor joist count and cost, or find the maximum allowable span, per Eurocode 5 (EN 1995) and the UK National Annex.Plywood Calculator →Calculate how many plywood sheets you need, using the standard 2440x1220mm metric sheet size.Roof Pitch Calculator →Convert roof rise and run into pitch as a percent grade, degrees, or ratio, plus rafter length.
Structural
Beam Deflection Calculator →Calculate maximum beam deflection for simply-supported or cantilever beams, with a deflection-limit pass/fail check.Beam Load Calculator →Calculate support reactions, shear force, and bending moment for a simply-supported beam carrying multiple point loads.Bending Stress Calculator →Calculate bending stress or applied moment using the flexure formula for common cross-sections, with a utilization-ratio check.Snow Load Calculator →Calculate roof snow load per Eurocode 1 (EN 1991-1-3) and the UK National Annex snow-load map, with a roof-capacity pass/fail check.
HVAC, energy & flow
CFM Calculator →Work out the ventilation airflow you need in CFM or m³/h for any room, based on recommended air changes per hour.Air Changes Per Hour Calculator →Work out the ACH a room is actually getting from its size and measured airflow, and check it against the recommended target.Heat Loss Calculator →Calculate a room’s fabric heat loss in watts to size a radiator correctly, using U-values in line with Building Regs Part L practice.Air Con Size (BTU) Calculator →Find the right air con size in BTU/hr and kW for your room from its floor area, sunlight, ceiling height and occupancy.Insulation Calculator →Calculate the total R-value and U-value (W/m²K) of a multi-layer wall, roof or loft insulation build-up.Gallons Per Minute (GPM) Calculator →Convert flow rate between US/UK gallons per minute and litres per minute, or solve for volume or time from a known flow rate.Pipe Volume Calculator →Calculate the internal fluid volume and liquid mass of a straight pipe from its inner diameter, length and liquid density.Tank Volume Calculator →Calculate the total and partial-fill capacity of a vertical cylinder, horizontal cylinder, rectangular or capsule-shaped tank, in litres or gallons.
Surfaces & finishes
Flooring Calculator →Calculate how much flooring you need for a room in m², with material-specific waste allowance and total cost.Tile Calculator →Calculate how many tiles and boxes you need for a floor or wall, including grout gap, layout pattern and waste allowance.Grout Calculator →Calculate how many bags of grout you need for a tiled area from tile size, joint width and depth, and grout type.Tile Adhesive Calculator →Calculate how many bags of tile adhesive you need for a tiling job, with thickness looked up by tile size.Plasterboard Calculator →Calculate how many plasterboard sheets you need for a room from wall/ceiling area, door and window openings, sheet size and waste allowance.Wallpaper Calculator →Calculate how many rolls of wallpaper you need for a room, using the standard UK roll size (0.52 x 10 m) and pattern repeat.Paint Calculator →Calculate how many litres of paint you need for a room from wall area, number of coats and coverage rate.Epoxy Calculator →Calculate how much epoxy resin and hardener you need for a rectangular or circular surface, at any mix ratio and coating thickness.Sealant Calculator →Calculate how many tubes or cartridges of sealant you need for a joint or gap from its length, width and depth.Roofing Calculator →Calculate your roof’s sloped surface area from its footprint and pitch, then estimate material and cost for tile, slate, metal or membrane roofing.Roof Shingle Calculator →Calculate how many bundles of asphalt shingles you need for a roof (an imported roofing style in the UK, distinct from the more common tile/slate roof).
Outdoor & fencing
Fence Calculator →Work out how many fence posts, rails, pickets and concrete for footings you need for your UK garden fence, plus total material cost in GBP.Fence Picket Calculator →Calculate exactly how many fence pickets you need from picket width and gap spacing, plus material cost in GBP.Board on Board Fence Calculator →Calculate posts, rails and overlapping boards for a board-on-board (featheredge-style) privacy fence, plus material cost in GBP.Decking Calculator →Calculate how many decking boards and fasteners you need for your deck, plus material cost in GBP.Block Paving Calculator →Calculate how many paving blocks you need for a driveway or patio from area and block size, including waste allowance and installed cost in GBP.Pool Volume Calculator →Calculate your swimming pool volume in litres or cubic metres and an estimated water-fill cost in GBP.Round Pen Calculator →Work out how many fence panels you need for a round pen from its diameter and panel length, plus cost in GBP.
Mechanical & electrical
Thread Calculator →Calculate metric screw thread geometry — pitch diameter, minor diameter and ISO 965 tolerances — from major diameter and pitch.Thread Pitch Calculator →Work out metric thread pitch from a measured length and thread count, and match it to the nearest standard ISO metric size.Bolt Torque Calculator →Calculate bolt tightening torque from clamping force using K-factor, diameter and lubrication factor, with an ISO 898-1 torque table.Welding Calculator →Calculate fillet or butt weld load capacity from leg size, length and base-metal strength, with a typical callout cost in GBP.Box Fill Calculator →Check an electrical enclosure against its rated fill capacity from conductor count, gauge, devices and grounds — IEC/CENELEC 60670 framing for the UK.
Contractor status & IR35-style calculators
IR35 Calculator: Cost of Being Inside vs Outside IR35 (2026/27) →Work out the true cost of IR35 status in 2026/27 – compare inside vs outside take-home, including employer NI, apprenticeship levy, pension and student loan.Inside IR35 Take-Home Pay Calculator (2026/27) →Calculate your inside-IR35 take-home pay for 2026/27 from a day or hourly rate, via agency PAYE or an umbrella company, with pension and student loan options.Outside IR35 Take-Home Pay Calculator (2026/27) →See your outside-IR35 limited company take-home for 2026/27, with an optimised salary/dividend split, VAT flat rate, expenses and pension contributions modelled.Inside vs Outside IR35 Comparison Calculator (2026/27) →Compare inside vs outside IR35 take-home pay side by side for 2026/27 and find the exact day rate that makes inside IR35 worth as much as outside.IR35 Back Tax / HMRC Settlement Calculator →Estimate a multi-year IR35 back-tax settlement – PAYE, employer and employee NI, HMRC interest and penalty bands – if HMRC reclassifies your contract.IR35 Deemed Payment Calculator (2026/27) →Work out your Chapter 8 IR35 deemed payment for 2026/27, step by step, including the 5% expenses allowance, pension contributions and employer NI.Spouse Dividend Splitting (S660A) Calculator →See how much tax a couple could save by splitting company dividends between spouses, with an Arctic Systems / S660A compliance checklist.
Contract vs. permanent comparisons
Salary to Day Rate Calculator →Convert a permanent salary into an equivalent contractor day rate for 2026, itemising pension, holiday, sick pay and employer NI you'd give up.Day Rate to Salary Calculator →Convert a contractor day rate into an equivalent permanent salary, comparing net income both ways with pension and holiday pay made explicit.Contract Comparison Calculator (Two Rates) →Compare two contract offers on take-home pay, even across different statuses – inside IR35, outside IR35 or umbrella – after expenses and pension.Salary Comparison Calculator (Two Salaries) →Compare two salaries side by side for 2026/27, including pension, bonus and car allowance, and see how frozen tax thresholds affect a pay rise.Umbrella Company Take-Home Pay Calculator (2026/27) →Calculate umbrella company take-home pay for 2026/27 from your day rate, including margin, employer NI, apprenticeship levy and April 2026 JSL agency-liability rules.
Contractor payroll & dividend tax
PAYE & National Insurance Calculator (2026/27) →Calculate Class 1 employee and employer National Insurance for 2026/27, including the 15% employer rate and Employment Allowance.Dividend Tax Calculator (2026/27) →Calculate 2026/27 dividend tax on salary plus dividends using the £500 allowance and the new 10.75%/35.75%/39.35% rates after April 2026's 2pp rise.
Small business & VAT
Limited Company Profit, Tax and Dividend Calculator (2026/27) →Turn contract profit into corporation tax, salary and dividends for 2026/27, with an optimal director salary/dividend split under the new dividend rates.VAT Calculator (Add / Remove VAT) →Add or remove VAT at the standard, reduced or zero rate, and check the £90,000 registration threshold for your contracting business.
Contractor financial planning
Contractor Mortgage Affordability Calculator →Estimate how much a contractor can borrow from a day rate, limited company accounts or umbrella payslips, with lender-style income multiples.Mortgage Payment and Net Income Impact Calculator →See a monthly mortgage payment as a share of your contractor or permanent take-home pay, with interest rate rise stress-test scenarios.Contractor Pension (SIPP) Calculator →Compare employer pension contributions through your limited company against personal SIPP contributions, with £60,000 annual allowance and carry-forward.Life Insurance Needs Calculator →Work out how much life cover you need based on income and debts, and compare paying premiums personally versus through a relevant life policy via your Ltd.Contractor Financial Profile Calculator →Score your contractor finances – war-chest months, pension adequacy and protection gaps – benchmarked by day-rate band, with fixes for weak areas.Permanent Employee Financial Profile Calculator →Get an instant financial health score from your salary – savings rate, pension adequacy and protection gaps – without a long budgeting form.
Target income & budget impact
Target Income Day Rate Calculator →Work backwards from your target net income to the day rate you need to charge, under umbrella, inside-IR35 or outside-IR35, with billable-days sliders.Required Salary Calculator →Reverse-calculate the gross salary needed to take home a target net amount in 2026/27, with a warning on frozen-threshold fiscal drag.Budget / Tax Year Change Impact Calculator →See the personal £/year impact of the latest Budget – dividend tax rises, frozen thresholds and umbrella JSL rules – on contractor and permanent income.Late Payment Interest Calculator (Statutory) →Calculate statutory interest on overdue invoices at 8% plus the Bank of England base rate, plus the £40-£100 fixed compensation sum, across multiple invoices.
