Percentage Calculators

Picking the right percentage tool

Nearly every percentage problem involves three quantities — a base, a rate and a result — and you always know two of them. The tools on this page differ only in which two you start with. If you have a rate and a base and want the slice, such as a 15% tip on a $64 bill, the general Percentage Calculator answers it and can also run the question backwards to find the rate or the base.

If you have two measurements taken at different times — last year's rent and this year's, a stock price at purchase and today — the base is the earlier figure and you want the rate. That is the job of the Percentage Change Calculator, which also reports the plain difference so a big-sounding rate on a tiny base does not mislead you.

When the rate is known and you need the new figure, choose by direction. Pay rises, markups, tips and sales tax push a number up, so use the Percentage Increase Calculator. Discounts, depreciation and budget cuts pull it down, so use the Percentage Decrease Calculator. Splitting these into two pages keeps the inputs unambiguous: you never have to remember whether to type a minus sign.

Three traps these calculators help you avoid

The wrong base. A shirt cut from $50 to $40 is 20% cheaper, yet going back from $40 to $50 is a 25% rise. The figure you divide by changes the answer, and each tool labels the base clearly.

Adding rates that should multiply. Two successive 10% rises lift a value by 21%, not 20%, and a 30% sale followed by an extra 20% off is a 44% total discount. Running one step at a time and feeding each result into the next calculation gets this right automatically.

Confusing points with percent. A mortgage rate moving from 6% to 7% is one percentage point higher but about 16.7% higher in relative terms. When the quantities you compare are themselves percentages, decide which of those two statements you mean before you report it.

How results are shown

Every percentage page gives the headline answer in large type, then the formula line with your numbers substituted, then a simple visual: a filled bar for shares of a whole, or a pair of bars comparing the starting and ending values. Figures keep full precision internally and are rounded only for display, to at most four decimal places with thousands separators, so you can copy them into a spreadsheet without accumulated rounding error.

Negative values and decimals are accepted wherever they make mathematical sense. You can find the percent change of a loss shrinking from −200 to −50, or apply a 2.75% increase. Where an operation is impossible — a change measured from zero, or a share of a zero total — the tool explains why instead of showing "Infinity" or "NaN".

Related tools

Percentages often sit next to other arithmetic. To turn a fraction such as 3/8 into a percent, find its decimal with the Fraction Calculator and multiply by 100. To combine several percentage scores into one overall mark when they carry different weights, the Grade Calculator handles the weighting for you.