Percentage Calculator

Solve any percentage problem in seconds: find a percentage of a number, work out what percent one number is of another, calculate percentage change, or increase or decrease a number by a percentage.

20% of 150
30
How it was calculated
  1. Convert the percentage to a decimal: 20 ÷ 100 = 0.2
  2. Multiply by the number: 0.2 × 150 = 30

How to use the percentage calculator

Choose the type of problem from the menu, enter your two numbers and the answer appears instantly with step-by-step working. The calculator handles the five most common percentage questions:

  • What is X% of Y? — e.g. a 20% tip on a $150 bill.
  • X is what percent of Y? — e.g. you scored 30 out of 150.
  • Percentage change — e.g. a price that rose from $50 to $65.
  • Increase or decrease by X% — e.g. adding 15% to 80.
  • Percentage difference — comparing two values when neither is the "original".

Percentage formulas

X% of Y = (X ÷ 100) × Y X as a % of Y = (X ÷ Y) × 100 Percentage change = (new − old) ÷ |old| × 100 Increase by X% = Y × (1 + X ÷ 100) Decrease by X% = Y × (1 − X ÷ 100) Percent difference = |A − B| ÷ ((A + B) ÷ 2) × 100

Worked examples

What is 20% of 150?

20 ÷ 100 = 0.2, and 0.2 × 150 = 30.

30 is what percent of 150?

30 ÷ 150 = 0.2, and 0.2 × 100 = 20%.

What is the percentage change from 50 to 65?

The difference is 65 − 50 = 15. Then 15 ÷ 50 = 0.3, so the change is +30% (an increase).

Increase 80 by 15%

80 × 1.15 = 92. To decrease 80 by 15% instead: 80 × 0.85 = 68.

Percentage change vs. percentage difference

Percentage change compares a new value with an original value, so direction matters: going from 50 to 65 is +30%, but going from 65 to 50 is −23.08%. Percentage difference compares two values on equal terms by dividing by their average, so the order doesn't matter: the difference between 40 and 60 is 40% either way.

Mental math shortcuts

  • 10%: move the decimal point one place left (10% of 250 = 25).
  • 5%: half of 10% (5% of 250 = 12.5).
  • 1%: move the decimal two places left (1% of 250 = 2.5).
  • Swap trick: X% of Y equals Y% of X — 8% of 50 is the same as 50% of 8, which is 4.

Frequently asked questions

How do I calculate a percentage of a number?

Divide the percentage by 100 to get a decimal, then multiply it by the number. For example, 15% of 200 is 0.15 × 200 = 30.

How do I calculate percentage increase?

Subtract the original value from the new value, divide the result by the original value, and multiply by 100. From 40 to 50 is (50 − 40) ÷ 40 × 100 = 25% increase.

How do I find what percent one number is of another?

Divide the first number by the second and multiply by 100. For example, 45 out of 60 is 45 ÷ 60 × 100 = 75%.

What is the difference between percent and percentage points?

Percentage points measure the simple difference between two percentages. If a rate rises from 4% to 5%, it increased by 1 percentage point, which is a 25% relative increase.

Why is a 50% increase followed by a 50% decrease not the original number?

Because each percentage applies to a different base. 100 increased by 50% is 150, but 50% of 150 is 75, so decreasing gives 75, not 100.

Results are rounded for display. For academic or professional work, double-check critical calculations and follow the rounding rules your teacher, school or organization requires.

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