Calculators
Percentage Calculator
The three percentage questions everyone asks — % of a number, X as a % of Y, and % change — answered instantly with the reasoning visible.
In short
Three percentage problems in one tool: find X% of Y, what percent X is of Y, and the percentage change between two numbers — instantly, with the work shown.
By NaveenKumar T · Updated
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- X% of Y
- X is what % of Y
- % increase / decrease
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One tool, three distinct questions
Most percentage mistakes come from solving the wrong problem: tip math is percent-of, score reporting is what-percent, and growth metrics are percent-change. The mode selector makes the choice conscious, and the result card phrases the answer in sentence form so a misread is obvious immediately.
The change mode deserves special respect — it's the one with a sign convention and an asymmetric inverse. Going 200 → 250 is +25%; going 250 → 200 is −20%; they are not mirror images. When the direction of comparison matters (it always does), put the starting value in X. The US Bureau of Labor Statistics uses the same percent-change formula to adjust contracts and benefits for inflation.
Worked example: all three modes
One set of numbers, run through all three questions:
| Question | Inputs | Result |
|---|---|---|
| X% of Y | 15% of 240 | 36 |
| X is what % of Y | 45 is what % of 180 | 25% |
| % change from X to Y | 80 → 100 | +25% |
Percentage points versus percent
The gap between the two grows as the starting value shrinks — a small percentage-point move can be a large percent move:
| From | To | Percentage-point change | Percent change |
|---|---|---|---|
| 5% | 7% | +2 points | +40% |
| 40% | 42% | +2 points | +5% |
| 50% | 48% | −2 points | −4% |
| 2% | 4% | +2 points | +100% |
Sources
Help
Frequently asked questions
Everything you need to know about the Percentage Calculator.
01How do I calculate the percentage increase or decrease between two numbers?
Subtract the old value from the new one, divide by the old value, and multiply by 100: ((new − old) ÷ old) × 100. From 80 to 100 is (20 ÷ 80) × 100 = +25%; from 100 to 80 is (−20 ÷ 100) × 100 = −20%. The two are not mirror images because the base changes, which is why the % change mode asks which number is the starting value.
02What formulas do the three modes use?
Percent-of: (X ÷ 100) × Y. What-percent: (X ÷ Y) × 100. Percent change: ((Y − X) ÷ X) × 100, signed — positive is an increase, negative a decrease. All three accept decimals and negative values where they're meaningful.
03Why isn't a 50% drop fixed by a 50% rise?
Because percent change is relative to the starting value, which shrinks after a drop. Fall from 100 to 50 (−50%), and recovering to 100 from a base of 50 requires +100%. The asymmetry trips up everything from grade curves to stock charts — the % change mode makes the direction and base explicit.
04What is the difference between percentage points and percent?
A percentage point is a raw subtraction of two percentages; a percent change is that difference divided by the starting percentage. A rate moving from 5% to 7% is up 2 percentage points, but it is a 40% increase in the rate itself ((7 − 5) ÷ 5 × 100). News coverage of interest rates, tax rates and survey results mixes the two constantly — check which one a headline means before reacting to it.
05How do I find the original number when I know the percentage?
Divide the part by the percentage as a decimal: original = part ÷ (percent ÷ 100). If 36 is 15% of some number, that number is 36 ÷ 0.15 = 240 — the reverse of the percent-of mode above.
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