Choose a Percentage Calculation
1 X is what % of Y?
25 is 12.5% of 200
2 What is X% of Y?
20% of 150 is 30
3 Y is X% of what number?
18 is 30% of 60
4 % Increase / Decrease
Change: 25%
Increase
Visual Comparison — Part vs Whole
Updates with the calculator you last usedHow These Percentage Calculations Work
A percentage is simply a fraction expressed out of 100. All four tools above use the same underlying relationship, rearranged for whichever value you need to find.
Percentage (%) = (Part ÷ Whole) × 100
One formula, three ways
| Tool | Solves for | Example |
|---|---|---|
| 1 | Percentage, given part & whole | 25 is what % of 200? → 25 ÷ 200 × 100 = 12.5% |
| 2 | Part, given percentage & whole | 20% of 150 → 20 ÷ 100 × 150 = 30 |
| 3 | Whole, given part & percentage | 18 is 30% of what? → 18 ÷ 0.30 = 60 |
| 4 | % change between two values | ((New − Old) ÷ Old) × 100 |
Why reversing a percentage change isn't symmetric
Suppose a shirt's price rose from ₹200 to ₹250 — that's a 25% increase: ((250 − 200) ÷ 200) × 100 = 25%. To fall back to ₹200, ₹250 only needs to drop by 20%, not 25%: ((200 − 250) ÷ 250) × 100 = −20%. The absolute change (₹50) is the same both times, but it's a bigger percentage of the smaller starting number and a smaller percentage of the larger one — which is why a percentage increase and the decrease that reverses it are never equal.
How to calculate a percentage, step by step
- Decide whether you need the percentage itself, a part of a whole, the whole given a part, or a percentage change between two values.
- Choose the matching tool on this page — "X is what % of Y", "X% of Y", "X is Y% of what", or "% change".
- Enter your known values into the tool's input fields.
- Click Calculate to see the result, with the calculation shown so you can check the working.
Common uses
- Calculating discounts, GST, tips and markups.
- Working out exam scores, attendance percentage or salary hikes.
- Comparing growth or decline between two periods (sales, population, prices).
Frequently Asked Questions
Because percentage change is always calculated against the current base value, and that base changes after the first move. ₹200 rising 25% becomes ₹250 — but to fall back to ₹200, ₹250 only needs to drop by 20%, not 25%, because that 20% is now a percentage of the larger ₹250 base. The same absolute ₹50 change is a bigger percentage of the smaller number and a smaller percentage of the larger number — which is why a percentage increase and the percentage decrease that reverses it are never equal.
Use ((New − Old) ÷ Old) × 100. A positive result means an increase, a negative result means a decrease. For example, a price rising from ₹200 to ₹250 gives ((250 − 200) ÷ 200) × 100 = 25%, an increase. Always divide by the Old (starting) value, not the New value — dividing by the wrong one is the most common percentage-change mistake.
All percentage problems come from the same relationship — Percentage = (Part ÷ Whole) × 100 — just rearranged depending on which value is unknown. If you know the part and whole, solve for percentage directly. If you know the percentage and whole, multiply to find the part. If you know the part and percentage, divide to find the whole. It's one formula, algebraically rearranged three ways.
Divide the part by the whole, then multiply by 100: (Part ÷ Whole) × 100. For example, to find what percentage 25 is of 200: 25 ÷ 200 × 100 = 12.5%.
Divide the part by the percentage expressed as a decimal: Part ÷ (Percentage ÷ 100). For example, if 18 is 30% of an unknown number, the whole is 18 ÷ 0.30 = 60.
A percentage point is the simple arithmetic difference between two percentages, while a percentage change measures relative change. If an interest rate moves from 5% to 6%, that's a rise of 1 percentage point, but a 20% percentage increase in the rate itself (since (6−5)÷5×100 = 20%). Mixing these two up is a common source of confusion in news headlines about rates and statistics.
A discount reduces a price by a percentage of itself — e.g. 20% off ₹500 removes 20% of 500 = ₹100, leaving ₹400. GST adds a percentage on top — e.g. 18% GST on ₹500 adds 18% of 500 = ₹90, making the total ₹590. Both use the "percentage of a whole" calculation (Tool 2 on this page), just added or subtracted depending on whether it's a charge or a discount.