Why is percent change from 100 to 80 equal to -20%, not -25%?

Change is measured from the starting value: (80-100)/100 = -0.20. Going back up from 80 to 100 is +25% because the base is different.

Not for "is what % of Y" or percent change from zero. Those divide by Y or the start value.

Does this handle currency?

Yes for simple percentages. Enter amounts without currency symbols (45 or 45.00).

Display uses standard half-up rounding to a few decimals. Keep more precision yourself if required.

Education

Percentage Calculator

Find a percentage of a number, reverse a percentage, or calculate percent change. Clear formulas show each step.

Mode

First number (X)

Second number (Y)

Results update as you type.

Last updated 3 October 2026

Choose a mode, enter the two numbers, and read the live result. Use Reset to clear fields.

What is X% of Y:     result = (X / 100) × Y
X is what % of Y:    pct = (X / Y) × 100
Percent change:      change = ((Y - X) / |X|) × 100

What is 20% of 60? → 12. (Tax tip: 8% of $45.00 → $3.60.)
25 is what % of 200? → 12.5%. A score of 45/50 is 90%.
Percent change from 80 to 100 → +25% (increase). From 100 to 80 → -20% (decrease).

Inputs must be finite numbers (commas are stripped).
"Of" mode rejects negative percentages.
Percent change uses absolute value of the starting number in the denominator so direction is shown by the sign.
Rounding shown to up to 4 decimal places; use the raw math for accounting-critical work.

Why is percent change from 100 to 80 equal to -20%, not -25%?: Change is measured from the starting value: (80-100)/100 = -0.20. Going back up from 80 to 100 is +25% because the base is different.
Can Y be zero?: Not for "is what % of Y" or percent change from zero. Those divide by Y or the start value.
Does this handle currency?: Yes for simple percentages. Enter amounts without currency symbols (45 or 45.00).
Is banker's rounding used?: Display uses standard half-up rounding to a few decimals. Keep more precision yourself if required.