What Is a Percentage Calculator?

A percentage calculator is a tool that handles the most common percentage maths people encounter every day — working out discounts, calculating a pay rise, figuring out how much VAT to add to an invoice, or checking by how much a price has increased. This calculator covers eight different percentage modes so you can answer any question instantly without needing to remember formulas.

How to Calculate a Percentage of a Number

To find X% of a value, divide X by 100 and multiply by the value. For example, 15% of £240 = (15 ÷ 100) × 240 = £36. This is useful for calculating discounts, tips, commission, or interest.

Common UK examples:

A shop offering 20% off a £75 item: 20% of £75 = £15 saving → you pay £60.
A 5% pension contribution on a £32,000 salary: 5% of £32,000 = £1,600 per year.
10% service charge on a £48 restaurant bill: 10% of £48 = £4.80.

What Percentage Is X of Y?

To express X as a percentage of Y, divide X by Y and multiply by 100. For example, if you scored 68 out of 80 in an exam: (68 ÷ 80) × 100 = 85%.

UK use cases:

Your business expenses were £4,200 of a £18,000 revenue month: 4,200 ÷ 18,000 × 100 = 23.3% expense ratio.
You repaid £2,500 of a £10,000 loan: 2,500 ÷ 10,000 × 100 = 25% paid off.

Percentage Increase and Decrease

Percentage increase shows how much a value has grown relative to the original. The formula is: ((New − Old) ÷ |Old|) × 100.

Percentage decrease works the same way but measures the fall: ((Old − New) ÷ |Old|) × 100.

UK salary example: Your salary rose from £28,000 to £31,500. Percentage increase = ((31,500 − 28,000) ÷ 28,000) × 100 = 12.5%. That's a meaningful rise — above the typical 3–4% cost-of-living increase seen in UK wage settlements in recent years.

House price example: A property bought for £220,000 is now worth £265,000. Increase = ((265,000 − 220,000) ÷ 220,000) × 100 = 20.45%.

Energy bill example: Your quarterly electricity bill fell from £380 to £310 after switching tariff. Decrease = ((380 − 310) ÷ 380) × 100 = 18.4% saving.

Percentage Difference

Unlike percentage increase or decrease, percentage difference is symmetric — it doesn't matter which number is "before" or "after". It compares two values against their average: |A − B| ÷ ((|A| + |B|) ÷ 2) × 100.

Use this when comparing two things of equal standing — for example, comparing two suppliers' quotes: £1,200 vs £1,450. Difference = (250 ÷ 1,325) × 100 = 18.87% apart.

Adding and Removing VAT

UK VAT is charged at 20% standard rate for most goods and services (5% reduced rate for domestic fuel/power; 0% for food and children's clothing). The calculator's "Add a %" and "Remove a %" modes handle both directions.

Adding VAT: A freelancer charges £500 net. VAT-inclusive price = £500 × 1.20 = £600. Use the "Add a %" mode with 20% to get the invoiced amount instantly.

Removing VAT (reverse calculation): You see a price of £840 including VAT and want the net figure. Net = £840 ÷ 1.20 = £700. The "Remove a %" mode does this in one step. This is essential for VAT-registered businesses calculating their input/output tax correctly.

Note: Simply taking 20% off a VAT-inclusive price is wrong. £840 × 0.80 = £672 — not £700. Always use the divide-by-1.20 method (or this calculator).

Percentage Change — Auto Direction

The "% Change" mode detects automatically whether the change is an increase or a decrease and labels the result accordingly. Useful when you have a before/after pair and just want to know the magnitude and direction without selecting the wrong mode.

UK-Specific Use Cases

Self Assessment: Calculating what percentage of your income goes to Income Tax or National Insurance. If you paid £6,200 tax on a £35,000 income: 6,200 ÷ 35,000 × 100 = 17.7% effective tax rate.
Making Tax Digital (MTD): When reconciling VAT returns, knowing the exact VAT-exclusive figure from a VAT-inclusive total is critical. Use "Remove a %" with 20%.
Stamp Duty: If your SDLT bill is £8,750 on a £350,000 purchase: 8,750 ÷ 350,000 × 100 = 2.5% effective SDLT rate.
Inflation: UK CPI rose from 100 to 118 between 2020 and 2024. That's an 18% cumulative increase — use the increase calculator to track purchasing power changes.
Business margins: Linked to the i24 Margin Calculator for full gross/net margin analysis.

Frequently Asked Questions

How do I calculate 20% of a number?

Divide the number by 5, or multiply by 0.2. Example: 20% of £350 = £350 ÷ 5 = £70. Alternatively, use the "% of a Number" tab above and enter 20 and 350.

What is the formula for percentage increase?

((New Value − Old Value) ÷ Old Value) × 100. The result is positive for an increase and negative if the value actually fell. The "% Increase" tab above handles this automatically.

How do I remove VAT from a price?

Divide the VAT-inclusive price by 1.20 (for 20% VAT). Do not subtract 20% — that gives the wrong answer. Use the "Remove a %" mode above and set the rate to 20.

What is the difference between percentage change and percentage difference?

Percentage change is directional — it measures how much one value moved from a starting point. Percentage difference is symmetric — it compares two values without implying one came "before" the other. Use change for time-series data; use difference when comparing two peers.

How do I calculate a percentage of a percentage?

Multiply the two percentages together and divide by 100. Example: 20% of 15% = (20 × 15) ÷ 100 = 3%. This comes up in compound interest and nested discount scenarios.

How do I work out a pay rise percentage?

Use the "% Increase" tab. Enter your current salary as "From" and your new salary as "To". The result is your percentage pay rise. Example: £27,500 → £29,000 = ((29,000 − 27,500) ÷ 27,500) × 100 = 5.45%.

What percentage of £100 is £17.50?

Use "What % is X of Y?": 17.50 ÷ 100 × 100 = 17.5%. This is also the basis of the old 17.5% VAT rate (2010 and earlier).

This calculator is free to use with no account required. For business invoicing, VAT returns, and financial tracking, see Invoice24 UK.