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Percentages turn up constantly — a discount in a sale, a pay rise, a share of a total, a change in a bill. This calculator handles the three questions that cover almost all of them, and shows the arithmetic behind each answer.
It is plain arithmetic, so there are no rates or tax years involved and the result never goes out of date.
Last reviewed
250% of 20
50
Each mode answers a different question, so the headline figure means something different in each case. In “percentage of a number”, the headline is the amount that the percentage represents, with the increased and decreased totals shown beneath it — useful for adding a service charge or taking a discount off a price.
In “percentage change”, the headline is the size of the movement relative to the original value, expressed as a signed percentage. A negative figure is a fall. In “number as a percentage”, the headline tells you what share one figure is of another.
All three modes come from the same relationship between a part, a whole and a rate.
A coat is listed at £250 and there is a 20% discount.
The discount is £50 and the sale price is £200.
Annual pay moves from £32,000 to £34,400.
That is a 7.5% increase.
You spent £312 on food out of a £1,200 monthly budget.
Food accounted for 26% of the budget.
The result depends on the following. If any of them do not match your situation, treat the figure as indicative only.
The calculation runs in the browser as a small set of pure TypeScript functions with no external library and no network request. Each function is covered by unit tests that assert the expected value for ordinary inputs, zero inputs and negative inputs.
Because the arithmetic is exact and rate-free, this calculator carries no tax year and no rate version. The “last reviewed” date reflects a check of the explanatory content rather than of any official figures.
A move from 4% to 6% is a rise of two percentage points, but a 50% increase in relative terms. Use percentage points when comparing two percentages directly, and percentage change when describing growth relative to a starting figure.
Each percentage is applied to a different base. £100 rising 20% gives £120; falling 20% from £120 removes £24, leaving £96. Percentage changes are multiplicative, not additive.
Divide rather than subtract. To remove a 20% uplift from £120, divide by 1.2 to get £100. Subtracting 20% of £120 would remove too much.
It can do the arithmetic, but the VAT calculator is the better tool because it applies the correct UK rate and shows the net, VAT and gross figures separately.
Please note: Results are estimates for general information only and are not financial, tax or legal advice. Figures depend on the assumptions listed on each page and on your personal circumstances.