Percentage of a Number

This calculator tells you what a given percentage of a number is and, in the same step, shows the number with that percentage added and subtracted. It covers everyday jobs like sale prices, tips, markups and pay raises.

How the calculation works

A percent is one hundredth, so the rule is simple: part = number × percent ÷ 100. Type the starting value into “Number” and the rate into “Percent”; the main result is the percentage amount. The unit doesn’t matter — dollars, pounds, miles or items — the answer comes back in the same unit as the number.

Two extra lines save you a second calculation. “Number + percent” equals number × (1 + p/100), which is a price after a markup, sales tax or raise. “Number − percent” equals number × (1 − p/100), which is a discounted price or an amount after a deduction.

Decimals, negative values and percentages above 100 are all accepted (up to 1,000%). A rate of 250% simply multiplies the number by 2.5; a negative rate flips the sign of the part, so the plus and minus lines swap.

Worked example

With the default inputs — number 1,000 and percent 10 — the part is 1,000 × 10 ÷ 100 = 100. The number plus 10% is 1,100 and the number minus 10% is 900. So a $1,000 laptop with a 10% discount costs $900, while a 10% markup takes it to $1,100.

Things to keep in mind

• Adding a percentage and then subtracting the same percentage does not bring you back: 1,000 + 10% = 1,100, but 1,100 − 10% = 990, because the second step uses a bigger base.
• To strip a percentage that is already included (for example a price that contains sales tax), divide instead of subtracting: $1,100 ÷ 1.10 = $1,000.
• Two successive 10% discounts are a 19% discount overall, not 20%: 1,000 × 0.9 × 0.9 = 810.
• Percentage points are not percents: a rate rising from 4% to 5% is up 1 percentage point, but 25% higher in relative terms.