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Three common percentage calculations in one tool: percent of a number, what percent one number is of another, and percent change.
A percentage calculator is a tool that handles the three most common percent problems people actually run into: finding a percent of a number (like a 20% tip on a $60 bill), figuring out what percent one value is of another (like 45 out of 180 on a test), and measuring the percent change between two values (like a price going from $50 to $75). The math itself is simple but easy to do backwards under pressure — swapping numerator and denominator, or confusing percent change with percentage-point change. This calculator picks the right formula for each mode so you get the right answer first try. Everything runs in your browser; nothing is sent to a server.
Use '% of a number' for tips, discounts, and commissions. Use 'What % is A of B' for scores and proportions. Use '% change' for price increases, growth rates, and year-over-year comparisons.
The first number, with meaning that depends on the mode: the percent rate, the part, or the starting value.
The second number: the base you're taking a percent of, the whole, or the ending value.
Your answer updates instantly. Two modes ('What %' and '% change') add a % suffix automatically so you don't have to remember the units.
% of a number: result = (percent ÷ 100) × base
e.g. 20% of 150 = 0.20 × 150 = 30
What % is A of B: result = (A ÷ B) × 100
e.g. 45 of 180 = 45/180 × 100 = 25%
Percent change: result = ((to − from) ÷ from) × 100
e.g. 50 → 75 = (75−50)/50 × 100 = +50%
(negative values indicate a decrease)Each mode rearranges the same underlying identity: part ÷ whole × 100 = percent. The difference is which of the three you're solving for. Percent change uses the starting value as the denominator by convention, which is why going from 100 to 50 is a −50% change but going from 50 to 100 is a +100% change — the two aren't symmetric. Don't confuse percent change with percentage-point change: a rate that moves from 4% to 6% is a 2 percentage-point increase but a 50% relative increase.
Reference: Wikipedia — Percentage
| Inputs | Result |
|---|---|
20% of 150 ('% of a number') | 30 0.20 × 150 = 30. Typical use: tip on a meal, sales tax on a purchase, commission on a sale. |
45 is what % of 180 ('What % is A of B') | 25% 45 ÷ 180 = 0.25. Typical use: test scores, attendance rates, proportions. |
From 50 to 75 ('% change') | +50% (75 − 50) ÷ 50 = 0.50. Going back from 75 to 50 is only −33.3% — percent change is asymmetric. |
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