Percentage Calculator
Calculate percentages, percentage of a number, and percentage change.
Three different questions, three different formulas — that is why percentage math goes wrong by hand. Pick the mode that matches your question: “X% of Y” for shares and discounts, “X is what percent of Y” for scores and ratios, or “percentage change” for growth and declines.
How it works
Percentages come up constantly -- working out a discount, checking exam scores, comparing growth between two periods -- but the three common percentage problems each use a different formula, which is where most manual calculation mistakes happen. This calculator handles all three in one place.
"X% of Y" answers questions like "what is 20% of 150?" -- useful for tips, discounts, and commission. "X is what percent of Y" flips that around: if you scored 42 out of 60, what percentage is that? And "percentage change" tells you the percent increase or decrease between an original value and a new one -- the calculation behind revenue growth, price changes, or year-over-year comparisons.
Just select the calculation type, enter your two numbers, and get an instant, exact result -- no need to remember which formula applies to which situation.
Worked examples
| Mode | Input | Result |
|---|---|---|
| X% of Y | 20% of 150 | 30 |
| X is what percent of Y | 42 out of 60 | 70% |
| Percentage change | 50,000 to 57,500 | +15% |
| Percentage change | 200 down to 150 | −25% |
Everyday uses
Salary hikes, exam marks, shop discounts, business growth and price changes are all the same three patterns: a share of a number, a ratio between two numbers, or movement from an old value to a new one.
For stacked price cuts use the discount calculator, and for tax-on-price math use the GST calculator — both build on the same percentage arithmetic.
Edge cases
Ratios and changes need a non-zero base: asking what percent of zero, or the change from a zero starting value, has no finite answer, so enter a non-zero X or Y for those modes. Percentage change uses the absolute value of the original, so the sign of the result always reflects direction — up or down — rather than the sign of the inputs.
Formula
Result = (X / 100) × Y
The share of Y that X percent represents — discounts, tips, commission.
Result = (X / Y) × 100
The ratio of X to Y as a percentage — exam scores, completion rates.
Result = ((Y − X) / |X|) × 100
Relative movement from the original X to the new Y; positive means increase, negative means decrease.
Frequently asked questions
How do I calculate percentage increase?
Use the 'percentage change' mode: enter the original value as X and the new value as Y. A positive result is an increase, negative is a decrease — for example, 50,000 to 57,500 is +15%.
How do I calculate percentage decrease?
The same 'percentage change' mode: enter the original value first. A fall from 200 to 150 shows as −25%.
What's the formula for 'X is what percent of Y'?
Divide X by Y and multiply by 100: (X / Y) × 100. For example, 42 out of 60 is (42/60) × 100 = 70%.
How do I find 20% of a number?
Use 'X% of Y' mode with X = 20 and Y = your number. The formula is (20/100) × Y — so 20% of 150 is 30.
Why is percentage change based on the original value, not the average?
Percentage change measures relative movement from a starting point, so it's always calculated against the original (X) value, not an average of the two -- this is the standard convention used in finance and statistics.
What is the difference between percentage change and percentage difference?
Percentage change is directional and anchored to the original value (50,000 → 57,500 is +15%). Percentage difference is symmetric — it compares two values against their average with no direction — and this calculator does not compute it.