UK Tools

Everyday Utilities

Percentage Calculator

Rates & guidance reviewed

Percentages appear everywhere — discounts, tax, tips, exam scores and growth rates. This free percentage calculator covers the most common everyday calculations in one place.

Work out X% of a number, what percent one number is of another, percentage change between two values, and reverse percentages. Ideal for shopping, budgeting and quick checks at work.

All maths runs in your browser with no tracking of the numbers you enter. For UK VAT at fixed rates, try the dedicated VAT calculator.

Interactive tool

Results

Result12.00

15.00% of 80.00

How to use this tool

  1. Pick the calculation type you need.
  2. Enter the numbers in the labelled fields.
  3. Read the result instantly as you type.
  4. Use related tools for money or unit conversions if needed.

Worked examples

Static sample calculations you can read without using the form. Figures match this tool's maths — always re-run with your own numbers for a personal estimate.

15% of 80

The default “what is X% of Y” calculation.

Inputs

Type
X% of a number
Percentage
15%
Of number
80

Results

Result
12.00

15% of 80 = 80 × 0.15 = 12.

18 is what percent of 90?

Part ÷ whole × 100.

Inputs

Type
Is what percent
Part
18
Whole
90

Results

Result
20.00%

Increase from 50 to 65

Percentage change between two values.

Inputs

Type
Percentage change
From
50
To
65

Results

Result
30.00%

((65 − 50) ÷ 50) × 100 = 30%.

Price now £80 after 20% off

Reverse percentage — find the original before a discount.

Inputs

Type
Reverse percentage
Final amount
80
Percentage change
−20%

Results

Original amount
100.00

£80 ÷ 0.8 = £100. For 20% UK VAT on a VAT-inclusive price, divide by 1.20 instead — or use the VAT calculator.

Common percentage mistakes

A 50% decrease followed by a 50% increase does not return you to the start — you end lower, because the increase applies to a smaller base. Percentage points (e.g. tax rising from 20% to 22%) are not the same as a percent change of the rate.

Reverse percentages are useful for “was/now” sales: if something is 20% off and now costs £80, the original is £80 ÷ 0.8 = £100. For VAT-inclusive prices at 20%, divide by 1.2 rather than subtracting 20% of the gross.

Frequently asked questions

How do I calculate X% of a number?
Multiply the number by X and divide by 100. Example: 15% of 80 = 80 × 0.15 = 12.
How do I calculate percentage increase?
((new − old) ÷ old) × 100. A rise from 50 to 65 is a 30% increase.
What is a reverse percentage?
Finding the original amount before a percentage change. If a price after 20% off is £80, the original is 80 ÷ 0.8 = £100.
Can I use this for VAT?
Yes for simple percentage maths. For UK 20%/5%/0% VAT add or remove with labelled net/VAT/gross, use our UK VAT Calculator.

Read the explainer

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