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Percentage Calculator

Study & Math

Find a percent of a number, work out what percent one number is of another, or measure the change between two values.

Your inputs

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The number, the part, or the starting value — depending on the mode.

The percentage, the whole, or the ending value — depending on the mode.

Result

Result —
  • Difference between A and B —
  • Ratio A : B —

Change any input and the result updates instantly.

Formula and rules

  • B% of A: result = A × B ÷ 100
  • A is what percent of B: result = A ÷ B × 100
  • Change from A to B: result = (B − A) ÷ |A| × 100, with a positive answer meaning an increase
  • Difference is the plain gap between the two values, ignoring direction

Worked examples

15% of 250

Input Mode B% of A, A 250, B 15.

Result 250 × 15 ÷ 100 = 37.5, and the gap between the two values is 235.

45 out of 180

Input Mode A is what percent of B, A 45, B 180.

Result 45 ÷ 180 × 100 = 25%, so 45 is a quarter of 180.

Change from 80 to 100

Input Mode percentage change, A 80, B 100.

Result (100 − 80) ÷ 80 × 100 = 25%, a 25% increase.

FAQ

What is the difference between percentage change and percentage points?

Moving from 10% to 15% is a 5 percentage point rise but a 50% increase, because the change is measured against the original 10%. Percentage points compare two percentages directly; percentage change compares against the starting figure.

Why does a drop from 100 to 80 show −20% while a rise back shows +25%?

Each change is measured against a different starting value: 20 off 100 is 20%, but 20 on 80 is 25%. That asymmetry is normal for percentage change and is why losses and gains of the same size do not cancel out.

Can I use negative or zero values?

Negative values are fine for a percent of a number and for ratios. Percentage change needs a non-zero starting value, and “A is what percent of B” needs a non-zero B, so the calculator reports an error when the divisor is zero.

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Disclaimer: Results follow the formula shown on this page and are for reference only. Real-world quantities vary with materials, technique and conditions, so allow a margin before ordering.