Students & Education
Percentage Calculator
Four common percentage questions in one place, answered as you type.
20% of 500
100
The remaining 80% is 400.
Percentage
20%
Of value
500
Free to use. No sign-up required.
How it works
A percentage is simply a fraction of 100. Every calculation on this page comes from that one idea: divide by the whole, multiply by 100.
Pick the mode that matches your question. "What is X% of Y" finds part of a total. "X is what % of Y" turns two numbers into a percentage. The increase and decrease modes compare a starting value with a new value and tell you how much it moved in percentage terms.
Percentage change is always measured against the original value, not the new one. That is why a rise from 100 to 150 is a 50% increase, while the fall back from 150 to 100 is a 33.33% decrease - the same absolute change, measured against different starting points.
Formula
What is X% of Y
(X ÷ 100) × Y
X is what % of Y
(X ÷ Y) × 100
Percentage increase
((new − original) ÷ original) × 100
Percentage decrease
((original − new) ÷ original) × 100
Worked examples
20% of 500 = 100
A 20% deposit on a 500 order. (20 ÷ 100) × 500 = 100, leaving 400 to pay.
100 is 20% of 500
You paid 100 towards a 500 total. (100 ÷ 500) × 100 = 20%, so you have covered a fifth.
100 → 125 is a 25% increase
A price rises from 100 to 125. ((125 − 100) ÷ 100) × 100 = 25% increase.
Frequently asked questions
Why is a 50% increase not cancelled out by a 50% decrease?
Because each is measured against a different starting number. 100 increased by 50% is 150. Taking 50% off 150 gives 75, not 100. The decrease is applied to the larger figure, so it removes more.
What happens if the original value is zero?
Percentage change cannot be calculated from zero, because it would mean dividing by zero. There is no meaningful percentage increase from nothing, so the calculator asks you for a non-zero starting value instead of showing a broken result.
Can I use decimals and negative numbers?
Yes. Decimals work everywhere. Negative values work too - percentage change from a negative starting value is measured against its size, so −50 to −25 registers as a 50% increase.
How many decimal places does it show?
Results are shown to two decimal places, with trailing zeros trimmed. The underlying calculation uses full precision, so no rounding error builds up.