Percentage calculator

Answer four everyday percentage questions as you type: X% of a number, what percent one number is of another, the percentage change between two numbers and the original number before a percentage.

By OpenBookMoney Editors · Free, no sign-up · Updated Oct 15, 2026

Percentage calculator

Four everyday percentage questions, answered as you type.

Percent of a number

What is % of ?
Answer 36
15% × 240 = 36

What percent is it?

is what % of ?
Answer 25%
45 ÷ 180 × 100

Percentage change

From to
Increase +15%
A difference of 12

Find the whole

is % of what?
Answer 300
36 ÷ 12%

How it’s calculated

X% of Y = X ÷ 100 × Y. X as a percent of Y = X ÷ Y × 100. Percentage change = (new − old) ÷ |old| × 100. If Y is X% of a number, that number = Y ÷ (X ÷ 100).

Results are rounded for display. Estimates only.

Percentage formulas, with examples

The four calculations, with simple examples.
QuestionFormulaExample
What is X% of Y?X ÷ 100 × Y15% of 80 = 12
X is what percent of Y?X ÷ Y × 10018 is 25% of 72
Percentage change from old to new(new − old) ÷ |old| × 100From 50 to 65 is a 30% increase
Y is X% of what number?Y ÷ (X ÷ 100)30 is 20% of 150

Type into any of the four rows and the answer updates instantly.

Everyday uses

  • Shopping: 25% off a $60 jacket saves $15, so you pay $45. For stacked discounts and sales tax, use our discount and sales tax calculator.
  • Pay raises: a raise from $52,000 to $54,600 is a 5% increase.
  • Original prices: if you paid $64 after a 20% discount, you paid 80% of the original price: $64 ÷ 0.80 = $80.
  • Tips: 18% of a $45 bill is $8.10. Our tip calculator also splits the bill.
  • Budgets: the 50/30/20 rule splits take-home pay into needs, wants and savings by percentage.

Percentages that trip people up

  • Percent vs. percentage points. A rate that rises from 4% to 5% goes up 1 percentage point, which is a 25% increase.
  • Ups and downs don’t cancel out. A price that rises 50% and then falls 50% ends 25% lower than where it started.
  • Stacked discounts multiply. 20% off and then another 10% off is 28% off in total, not 30%.
  • The base matters. “X is what percent of Y” and “Y is what percent of X” give different answers.

How to calculate a percentage in your head

Find 10% by moving the decimal point one place left, then build from there. For 15% of $80: 10% is $8, half of that (5%) is $4, so 15% is $12. For 20%, double the 10% figure.

Frequently asked questions

How do I calculate a percentage of a number?

Divide the percentage by 100 and multiply by the number. For example, 15% of 80 is 0.15 × 80 = 12.

How do I work out a percentage increase?

Subtract the old value from the new value, divide by the old value and multiply by 100. From 50 to 65: (65 − 50) ÷ 50 × 100 = 30%.

How do I find the original number before a percentage?

Divide the number by the percentage written as a decimal. If 30 is 20% of a number, the number is 30 ÷ 0.20 = 150.

Why does a percentage decrease look smaller than the same increase?

Because the starting value changes. Going from 100 to 150 is a 50% increase, but going back from 150 to 100 is only a 33.3% decrease.

Results are rounded for display.