How it works
Choose a mode (percentage of a number / what percent / increase or decrease), enter the values, and we compute it in your browser.
In detail
A percentage is a fraction of 100. This calculator handles the three everyday cases:
- X% of Y: Y × (X ÷ 100). E.g. 20% of 250 = 50.
- X is what % of Y: (X ÷ Y) × 100. E.g. 30 of 120 = 25%.
- Increase / decrease: ((new − old) ÷ old) × 100.
Useful for discounts, tips, tax slices (e.g. the VAT portion) and comparing figures. It is pure arithmetic — no data leaves your device.
This calculator provides estimates only. Tax rules, bands and rates change every tax year — verify against the official source (HMRC) or a qualified adviser before relying on any number.
FAQ
How do I find X% of a number?
Multiply the number by X divided by 100.
How do I work out what percent X is of Y?
Divide X by Y and multiply by 100.
How is percentage change calculated?
Subtract the old value from the new, divide by the old, then multiply by 100.
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