Percentage Change
How much a value grew or dropped in percent: divide the difference by the old value (that is the comparison base) and multiply by 100.
Solution
The main rule of percents. A percent is just one hundredth. So nearly every percent problem reduces to two actions: find 1% (divide by 100 or by the known number of percents) and multiply by however many you need. The calculator shows this in every mode: the formula, your numbers substituted, and a plain-words explanation.
FAQ
How do you find a percent of a number without a calculator?
Divide the number by 100 to get 1%, then multiply by the percent you need. For 15% of 80: 80 / 100 = 0.8, then 0.8 · 15 = 12. Handy trick: 10% is the number with its last digit shifted (8), 5% is half of that (4), so 15% = 8 + 4 = 12.
Why is percentage change computed from the old value?
Because the question is “by what percent did the original change”. The base is the original value. That is why growth from 100 to 150 is +50%, but a drop from 150 to 100 is −33%: the percentages there and back are not the same.
How do you get the number back from a percent?
If X% of a number equals Y, divide Y by X to get 1%, then multiply by 100. For example, 20% of a number is 30: 30 / 20 = 1.5, so the number is 150.
Percent vs percentage points — what is the difference?
If a rate goes from 10% to 12%, it rose by 2 percentage points but by 20 percent (2/10 · 100). Percent compares relative values; points measure the absolute difference between two percentages.
Free online percentage calculator with formulas and an explanation for every step. Four modes: percent of a number, what percent one number is of another, percentage change between two values, and recovering a number from a known percent.
Unlike plain calculators, this one shows how the answer comes about: the formula, your numbers substituted, and a plain-words explanation. A percent is one hundredth — and all four problems reduce to finding 1%.
Everything runs in the browser with no data sent to a server. Useful for school percent problems, discounts and markups, price changes, salaries, and metrics — anywhere you need percentages fast and with understanding.