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Percentage Calculator

Three common percentage problems in one tool — pick a mode and start typing.

Short answer

Pick the calculation type, fill in the two numbers, and the answer updates instantly. % of a number = (% / 100) × number. % change = (new − old) / old × 100.

Calculation

Fill in the fields above to see your result instantly.

Calculation method, coverage and version

Inputs used
What do you want to work out?, X, Y.
Calculation approach
The calculator applies the rules and assumptions described in “How it works” to the values you enter. Rounding can cause small differences from an official or provider calculation.
Coverage
Maths. UK nations, tax treatment, local rules and provider criteria can differ; check the official sources shown below before acting.
Content version
No page-specific review date is currently published. Treat the result as indicative and verify current rules independently.
Not included unless explicitly requested: personal circumstances not entered, provider discretion, future rule changes, professional fees and case-specific exceptions. Read the full calculator methodology.

How it works

Three formulas:

  • X% of Y = (X ÷ 100) × Y
  • X is what % of Y = (X ÷ Y) × 100
  • % change = ((Y − X) ÷ X) × 100

Worked example

20% of £150 = (20 ÷ 100) × 150 = £30.

£42 is what % of £200? (42 ÷ 200) × 100 = 21%.

£80 → £92 = ((92 − 80) ÷ 80) × 100 = +15%.

Who should use this

  • •Shoppers checking discounts and sale prices
  • •Anyone working out tips, tax or service charges
  • •Investors comparing returns

Common mistakes

  • ×Confusing 'percentage' with 'percentage points' — 4% to 6% is +2 percentage points but a +50% change
  • ×Calculating change from the wrong base — always divide by the original number

Frequently asked questions

What's the difference between % and percentage points?▾

If a rate goes from 4% to 6%, that's a 2 percentage point rise but a 50% increase.

Why is my answer slightly off?▾

Floating-point arithmetic can show tiny rounding errors. We round to 4 decimal places for display.

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