Percentage calculator

A percentage calculator with six sums on one page

This percentage calculator covers the six questions that come up in everyday life: x% of a number, what percent one number is of another, percentage change, an increase, a discount, and the original value before a change. All six blocks sit on the same page and each result updates as you type. The maths runs in your browser and there is no account to create.

How to calculate a percentage with the tool

1. Pick the block that matches your question, for example "Decrease by x% (discount)".
2. Replace the sample values with your own. Decimals can be typed with a point or a comma, and negative numbers are accepted.
3. Read the result at the end of the line. It is rounded to 4 decimal places at most.

The six formulas, each with a worked example

Percentage of a number: value × rate ÷ 100

A restaurant adds a 12.5% service charge to a £64 bill: 64 × 12.5 ÷ 100 = £8. In your head: 10% means dividing by 10, so £6.40; 2.5% is a quarter of that, £1.60; together, £8.

What percentage is it? a ÷ b × 100

You score 54 out of 72 in a test: 54 ÷ 72 × 100 = 75%. The same formula gives a pass rate or the share of rent in a monthly budget.

Percentage change: (new − old) ÷ old × 100

A monthly energy bill falls from £160 to £136: −24 ÷ 160 × 100 = −15%. When the value goes up, the tool shows a + sign in front of the result.

Increase by x%: value × (1 + rate ÷ 100)

A £32,000 salary with a 4% pay rise: 32,000 × 1.04 = £33,280. The tool also shows the amount added: "that is 1,280 more".

Decrease by x% (discount): value × (1 − rate ÷ 100)

Trainers priced at £85 with 20% off: 85 × 0.80 = £68, "that is 17 less". For 20 percent off, divide the price by 5 and take that away; for 25 percent off, take away a quarter.

Find the original value: value ÷ (1 + rate ÷ 100)

An invoice shows £150 including UK VAT at the standard 20% rate: 150 ÷ 1.2 = £125 before VAT. To get back to a price before a discount, enter a negative rate: 68 after a change of −20% gives 85.

Common mistakes with percentages

• A rise and a fall of the same rate do not cancel out. £100 + 20% = £120, then £120 − 20% = £96. The cut applies to a bigger base.
• Successive percentages do not add up. Two 10% rises give 100 → 110 → 121, which is 21%, not 20%.
• Percentage points are not percent. A rate that moves from 10% to 12% gains 2 percentage points, but it rises by 20%.
• Removing 20% VAT is not taking 20% off. You divide by 1.2: £120 including VAT is £100 before VAT. Taking 20% off would give £96, which is wrong.

Fractions and percentages side by side

Frequently asked questions

How do I calculate a percentage in my head?

Start from 10% (divide by 10) and 5% (half of that), then combine them: 15% is 10% plus 5%. Another trick: x% of y equals y% of x. So 16% of 25 is the same as 25% of 16, which is 4.

How do I work out the percent off between two prices?

Use the "Percentage change" block with the old price, then the new one: from 85 to 68, the tool shows −20%.

How should I type large numbers?

Type 32000, 32 000 or 32,000: spaces are ignored, and a comma followed by exactly three digits is read as a thousands separator. Otherwise a comma or a point marks the decimals, so 12.5 and 12,5 are the same. If in doubt, type large numbers without any separator.

Why does the result show a dash?

The sum cannot be done: an empty field, an entry that is not a number, or a division by zero, such as a share out of 0 or a change starting from 0.