Last updated: October 2026
How to calculate percentage increase
Short answer: subtract the old value from the new value, divide by the old value, and multiply by 100: (new − old) ÷ old × 100. Going from 50 to 75 is (75 − 50) ÷ 50 × 100 = 50% increase. Pick the "% Increase" mode above and it does the math as you type.
Percentage increase formula — worked example
The formula never changes, only the numbers:
% change = (new − old) ÷ old × 100
A shop raises a $200 jacket to $250. The increase is (250 − 200) ÷ 200 × 100 = 25%. The same formula handles drops too — if the jacket falls to $150, that's (150 − 200) ÷ 200 × 100 = −25%, a 25% decrease. Try both in the calculator's first two modes.
One textbook nuance: formal versions of the formula divide by the absolute value of the starting number — (new − old) ÷ |old| × 100. It only matters with negative starting values: going from −50 to −25 is a 50% increase by that convention ((−25 − (−50)) ÷ 50 × 100), since the value moved in the positive direction. Everyday cases use positive numbers, so you'll rarely need it.
Percentage decrease
Decrease uses the identical formula — the result is simply negative, and the calculator reports it as a positive "drop". One honest edge case: percentage change from zero is undefined, because the formula divides by the starting value. Going from 0 to anything is an infinite increase, so the tool shows a clear error instead of a fake number.
Common percentage calculations
Watch out for the classic trap: percentage points vs percent. Moving from 20% to 25% is a 5 percentage-point rise but a 25% percent increase (5 ÷ 20 × 100). And yes — a 100% increase exactly doubles a value.
Frequently asked questions
How do you calculate percentage increase?
Subtract the old value from the new value, divide by the old value, and multiply by 100: (new − old) ÷ old × 100. For example, going from 50 to 75 is (75 − 50) ÷ 50 × 100 = 50% increase. The calculator above does this instantly.
What is the formula for percentage decrease?
The same formula as increase: (new − old) ÷ old × 100 — the answer just comes out negative, and the calculator reports it as a positive percentage drop. Going from 200 to 150 is (150 − 200) ÷ 200 × 100 = −25%, i.e. a 25% decrease.
How do you find what percent one number is of another?
Divide the part by the whole and multiply by 100: X ÷ Y × 100. For example, 30 is what percent of 200? 30 ÷ 200 × 100 = 15%. Use the "X is what % of Y" mode in the calculator above.
How do you calculate X percent of Y?
Convert the percentage to a decimal and multiply: (X ÷ 100) × Y. For example, 20% of 150 is 0.20 × 150 = 30. Use the "X% of Y" mode in the calculator above.
Can you calculate percentage increase from zero?
No — percentage change from a starting value of zero is mathematically undefined, because the formula divides by the old value. Going from 0 to any number is an infinite increase. The calculator shows a clear error instead of a misleading number.
What is the difference between percentage points and percent?
A move from 20% to 25% is a 5 percentage-point increase, but a 25% percent increase (5 ÷ 20 × 100). Percentage points measure the absolute gap; percent measures the relative change. Mixing them up is one of the most common percentage mistakes.
What is the difference between percent increase and percent difference?
Percent increase measures change relative to a starting value: (new − old) ÷ old × 100. Percent difference measures how far apart two values are relative to their average: |a − b| ÷ ((a + b) ÷ 2) × 100 — direction doesn't matter. Use percent increase when there is a clear "before and after" (prices, growth); use percent difference when comparing two peers with no natural baseline (two measurements, two products).
Is a 100% increase the same as doubling?
Yes. A 100% increase means the value grew by its own full amount: 50 → 100 is +100%. A 200% increase triples it (50 → 150), and a 50% decrease halves it.
Is my data private?
Completely. Every calculation happens locally in your browser with JavaScript — your numbers are never sent to a server, stored, or tracked in any way.
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