Percentage Calculator
Pick the question that matches yours and type your numbers. Each answer updates instantly with the formula worked out.
Percentage of a number
What percent is X of Y?
Percentage increase or decrease
Add or subtract a percentage
Reverse percentage (find the original)
Percentage points vs percent
A percentage point is the plain difference between two percentages. A rate going from 4% to 5% rises by 1 percentage point, which is a 25% increase relative to where it started.
Percentage formulas
A percentage is a fraction of 100, so 15% means 15 ÷ 100 = 0.15.
- X% of Y = X ÷ 100 × Y. 15% of 200 = 30.
- X as a percent of Y = X ÷ Y × 100. 30 out of 200 = 15%.
- Percentage change = (new − old) ÷ |old| × 100. From 80 to 100 is a 25% increase; from 100 to 80 is a 20% decrease.
- Add X% = Y × (1 + X ÷ 100); subtract X% = Y × (1 − X ÷ 100). 250 plus 18% = 295.
- Reverse percentage: original = final ÷ (1 + X ÷ 100) for an increase, or ÷ (1 − X ÷ 100) for a decrease. A price of 118 including 18% GST was 100 before tax.
FAQ
Why isn't a 20% rise followed by a 20% fall back to the start?
Each percentage applies to a different base. 100 plus 20% is 120, and 20% of 120 is 24, so the fall leaves you at 96. Use the reverse calculator to find the value before a change.
How do I remove GST or VAT from a price?
Use the reverse percentage card with "more": enter the price including tax and the tax rate. Dividing by 1.18 removes 18% GST; simply subtracting 18% would take off too much.
What is the difference between percent and percentage points?
Percent describes a relative change; percentage points describe the absolute gap between two percentages. An interest rate moving from 4% to 5% is up 1 percentage point, or 25 percent.
Are my numbers sent anywhere?
No. Every calculation runs on your device in WebAssembly, and nothing is stored.