How to use the percentage calculator
Choose the question that matches what you're trying to work out, enter your numbers, and the result appears instantly. There's no Calculate button — every panel updates as you type, and your inputs are saved to your browser so they come back when you return.
What the six panels do
- X% of Y — "What is 15% of 200?" → 30.
- X is what % of Y — "30 is what percent of 200?" → 15%.
- X is Y% of what — the reverse question. "30 is 15% of what number?" → 200.
- Change A → B — percentage increase or decrease. "Price went from 80 to 100" → +25%.
- Difference A ↔ B — how far apart two values are. "Difference between 80 and 100" → 22.22%.
- Reverse % — you know the final value and the percent applied. "125 after a 25% increase" → 100.
The formulas
- X% of Y = (X ÷ 100) × Y
- X is what % of Y = (X ÷ Y) × 100
- X is Y% of what = X ÷ (Y ÷ 100)
- Change from A to B = ((B − A) ÷ A) × 100
- Difference = |A − B| ÷ ((A + B) ÷ 2) × 100
- Reverse = final ÷ (1 ± X ÷ 100)
Percentage change vs percentage difference
Percentage change measures movement from a specific starting value. Percentage difference compares two values without designating either one as the starting point. If 80 changes to 100, that's a 25% change. The difference between 80 and 100 is 22.22% because the average (90) is the reference.
Percentage points vs percent
If an interest rate goes from 5% to 7%, that's a 2 percentage point increase — but a 40% relative increase.
Common real-world uses
- Shopping discounts — "30% off" a ₹1,500 shirt means you pay ₹1,050.
- Tips and tax — adding 18% GST to a bill, or a 15% tip.
- Salary hikes — "went from 60,000 to 72,000" is a 20% increase.
- Investment returns — "portfolio dropped 12% this quarter".
- Grade calculations — "42 out of 50" is 84%.
Why use this tool?
Unlike online calculators that submit your numbers to a server, this one runs entirely in your browser. Nothing is uploaded, no account is needed, and it works offline after the first visit.
Common questions
How do I calculate X% of Y?
Multiply Y by X and divide by 100. For example, 15% of 200 is 200 × 15 ÷ 100 = 30.
How do I calculate percentage increase?
Divide the increase by the original value, then multiply by 100. Going from 80 to 100 is 25%.
How do I calculate percentage decrease?
Going from 100 to 80 is a decrease of 20, which is −20%.
What is the difference between percentage change and percentage difference?
Change uses a starting value. Difference compares two values without designating either as the start.
How do I reverse a percentage?
If increased, divide the final by (1 + X ÷ 100). If decreased, divide by (1 − X ÷ 100).
Are my inputs saved?
Yes. Your inputs are stored in your browser's local storage and restored when you return.