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Percentage Calculator
Work out percentages, ratios and growth rates.
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Processed locallyAbout Percentage Calculator
Common percentage questions — share, increase, decrease — as tabs: pick one and fill in two numbers.
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Four modes, each with its formula in the title: "X% of Y" (`X × Y ÷ 100`), "X is what percent of Y" (`X ÷ Y × 100`), "increase/decrease X by Y%" (two buttons), and "percent change from X to Y" (`(Y − X) ÷ X × 100`).
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The last one causes the most confusion: it is the change **relative to the starting value**, so it is order-sensitive — 100 → 120 is +20%, while 120 → 100 is −16.67%, and the two are not negatives of each other.
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Switching modes keeps your work: each of the four sets of inputs and results is preserved, so you can compare without retyping.
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Pick a mode
Choose by the question you are answering: a percentage of a number, a share, an increase/decrease, or a rate of change.
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Enter two numbers and calculate
The increase/decrease mode has two buttons, giving the raised and lowered values separately.
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Read the direction label
The change mode labels the result increase, decrease or no change, so you do not have to work out the sign.
Because the denominator is the **starting value**: going from 100 to 120 is a 20% rise, but falling back from 120 to 100 is only 16.67% (20 ÷ 120). That asymmetry is a mathematical fact, not a bug in the tool — a rise and a fall of the same absolute size never cancel out. A symmetric measure exists (percent difference, dividing by the mean of the two values) but it is rare in everyday use.
Both inputs must parse as numbers and the divisor cannot be zero — for "X is what percent of Y", a Y of 0 leaves the result empty rather than printing Infinity. The fields accept decimals and negatives as well, so watch out: a negative increase may point the opposite way from what you intended.
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