What Is a Percentage Calculator?

A percentage calculator takes the mental arithmetic out of everyday tasks — working out GST, calculating a discount at the Boxing Day sales, checking your superannuation contribution rate, or seeing how much house prices have moved in your suburb. This tool covers eight percentage modes so you can get an accurate answer instantly on any device.

How to Calculate a Percentage of a Number

Divide the percentage by 100 and multiply by the number. To find 15% of A$320: (15 ÷ 100) × 320 = A$48.

Australian examples:

10% GST on a A$450 product: 10% of A$450 = A$45 GST → total A$495.
11% compulsory superannuation on a A$70,000 salary: 11% of A$70,000 = A$7,700 per year (increasing to 12% by 2025–26).
25% off a A$199 pair of boots: 25% of A$199 = A$49.75 → you pay A$149.25.

What Percentage Is X of Y?

Divide X by Y and multiply by 100. If your quarterly BAS shows A$6,300 GST collected on A$69,300 turnover: 6,300 ÷ 69,300 × 100 = 9.09% — confirming your 10% GST exclusive figure is correct (A$63,000 × 10% = A$6,300).

Percentage Increase and Decrease

Formula: ((New − Old) ÷ |Old|) × 100.

Property example: You bought a property in 2019 for A$620,000 and it's now worth A$890,000. Increase = ((890,000 − 620,000) ÷ 620,000) × 100 = 43.5% capital growth.

Wage example: Your hourly rate increased from A$27.50 to A$29.70. Increase = ((29.70 − 27.50) ÷ 27.50) × 100 = 8% — matching Australia's recent Fair Work increases for award wages.

Cost of living: Australia's CPI rose substantially from 2021 to 2024. If your grocery spend increased from A$180/week to A$220/week: ((220 − 180) ÷ 180) × 100 = 22.2% increase.

Adding and Removing GST

Australia's Goods and Services Tax is a flat 10% on most goods and services. The ATO requires GST-registered businesses (turnover over A$75,000) to include GST in their prices and report it on their BAS.

Adding GST: A tradie quotes A$1,200 ex-GST for a job. Total with GST = A$1,200 × 1.10 = A$1,320. Use the "Add GST / %" tab with 10%.

Removing GST (reverse): A receipt shows A$385 including GST. Ex-GST amount = A$385 ÷ 1.10 = A$350. The GST component = A$35. Use the "Remove GST / %" tab — the common mistake of subtracting 10% directly gives A$346.50, which is wrong.

One-eleventh rule: The GST component of any GST-inclusive price is always 1/11th of that price. A$385 × (1/11) = A$35. This is a quick mental check.

Percentage Difference

Symmetric comparison between two values: |A − B| ÷ ((|A| + |B|) ÷ 2) × 100. Comparing two tradies' quotes — A$1,400 vs A$1,750: |350| ÷ 1,575 × 100 = 22.2% apart.

Australian-Specific Use Cases

Super contribution rate: From 1 July 2024, the Superannuation Guarantee rate is 11.5%. On A$80,000: 11.5% × A$80,000 = A$9,200 per year employer contribution.
Stamp duty: If stamp duty is A$22,490 on a A$550,000 property purchase: 22,490 ÷ 550,000 × 100 = 4.09% effective rate.
HECS-HELP repayments: If your repayment income is A$68,000 and your repayment rate is 3%: 3% of A$68,000 = A$2,040 annual repayment.
Margin scheme: For property developers using the GST margin scheme, percentage calculations help determine the taxable proportion of the margin.
Business invoicing: See Invoice24 Australia for GST-compliant invoicing and BAS preparation tools.

Frequently Asked Questions

How do I add GST to a price?

Multiply the ex-GST price by 1.10. Example: A$500 × 1.10 = A$550. Use the "Add GST / %" tab with 10% pre-filled.

How do I remove GST from a price?

Divide the GST-inclusive price by 1.10. Example: A$550 ÷ 1.10 = A$500 ex-GST. Do not subtract 10% — that gives the wrong answer (A$495, not A$500).

How do I calculate the superannuation contribution?

Multiply your ordinary time earnings by the current Super Guarantee rate (11.5% from 1 July 2024). On A$55,000: 11.5% × A$55,000 = A$6,325. Use the "% of a Number" tab.

How do I calculate the percentage change in house prices?

Use the "% Increase" tab. Enter the old price in "From" and the new price in "To". For A$750,000 → A$920,000: ((920,000 − 750,000) ÷ 750,000) × 100 = 22.67% increase.

What percentage of my income is my rent?

Use "What % is X of Y?". Enter your rent as Number 1 and your take-home income as Number 2. A$2,200 rent on A$6,500 take-home = 2,200 ÷ 6,500 × 100 = 33.8%. The standard affordability rule is under 30%.

How does the "% Difference" mode differ from "% Increase"?

Percentage increase is directional — it has a starting point. Percentage difference is symmetric — it doesn't matter which number is first. Use difference when comparing two things of equal standing, like two quotes or two prices today.

Free to use, no account needed. For GST-compliant invoicing and expense tracking, see Invoice24 Australia.