Quickly solve the three most common percentage problems: percent of a number, what percent one number is of another, and percentage change.
A percentage is simply a number expressed as a fraction of 100. The three calculators above cover the situations you run into most often.
Percent of a number: (Percentage ÷ 100) × Value. For example, 15% of 200 = 0.15 × 200 = 30.
What percent X is of Y: (X ÷ Y) × 100. For example, 30 of 120 = (30 ÷ 120) × 100 = 25%.
Percentage change: ((New − Old) ÷ Old) × 100. A jump from 100 to 125 is a 25% increase; a drop from 100 to 80 is a 20% decrease.
A key thing to understand about percentages is that increases and decreases are not symmetrical. If a $100 stock rises 50% to $150, then falls 50%, it doesn't return to $100 — it drops to $75, because the second 50% is calculated on the larger $150 figure. This is why you can't simply reverse a percentage change by applying the same percentage in the opposite direction. To undo a 50% increase you actually need a 33.3% decrease. Our percentage change tool above handles the direction automatically, so you always see whether the result is an increase or a decrease and by exactly how much.
People often confuse "percent" with "percentage points," and the difference can be significant. If an interest rate rises from 4% to 6%, that's an increase of 2 percentage points, but a 50% increase in relative terms (because 2 is half of 4). News headlines and reports mix these up constantly. When you want the relative change — how much bigger or smaller something got — use the percentage-change calculator above. When you simply want the arithmetic gap between two percentages, subtract them directly.
Percentages, decimals, and fractions are three ways of expressing the same value. To convert a decimal to a percentage, multiply by 100 (0.25 → 25%). To convert a percentage to a decimal, divide by 100 (25% → 0.25). To turn a fraction into a percentage, divide the top by the bottom and multiply by 100 (3/4 → 0.75 → 75%). Knowing these conversions makes mental math faster and helps you sanity-check the results from any calculator.
Divide the first number by the second and multiply by 100. For example, 30 out of 120 is (30 ÷ 120) × 100 = 25%. Use the "X is what percent of Y?" tool above to do it instantly.
Subtract the original value from the new value, divide the result by the original value, and multiply by 100. Going from 100 to 125 is ((125 − 100) ÷ 100) × 100 = a 25% increase.
Multiply the number by (1 + percentage/100). To add 15% to 200, calculate 200 × 1.15 = 230. To subtract a percentage, multiply by (1 − percentage/100) instead.
Percentage points are the simple arithmetic difference between two percentages, while a percentage change is relative. A move from 4% to 6% is 2 percentage points but a 50% increase.
No. Because each percentage applies to a different base, a 50% increase followed by a 50% decrease does not return you to the start. Undoing a 50% increase requires a 33.3% decrease.