Free Percentage Calculator
Work out percentages three ways, with the formula shown for each result.
How to use / FAQ
Pick a mode, enter two numbers, and the answer updates as you type — no equals button. Each result shows the exact formula used, so you can follow the maths or check it by hand.
The three modes cover almost every percentage question that comes up in practice. “What is X% of Y” handles discounts, tips, tax, and commission. “X is what percent of Y” turns raw numbers into a rate — a test score, a conversion rate, a share of a total. “Percentage change” measures growth or decline between two values: a price rise, a salary increase, month-over-month traffic. Because the formula is printed with every answer, the tool doubles as a worked example when you want to understand the calculation, not just get the number.
Which mode should I use?
Use 'X% of Y' to take a percentage of an amount, 'X is what % of Y' to turn a ratio into a percentage, and '% change' to measure an increase or decrease between two values.
How do I calculate a percentage by hand?
Divide the part by the whole and multiply by 100. If 34 of 40 answers are correct, 34 ÷ 40 = 0.85, so the score is 85%. Going the other way, X% of a number is the number times X divided by 100 — 15% of 80 is 80 × 0.15 = 12.
How is percentage change worked out?
It's the difference between the two values divided by the starting value, times 100. A negative result means a decrease. Note the direction matters: going from 100 to 150 is a 50% increase, but going from 150 back to 100 is only a 33.3% decrease, because the starting value changed.
How do I add or subtract a percentage, like tax or a discount?
Use 'X% of Y' to find the amount, then add or subtract it from the original. For 20% off £50, 20% of 50 is £10, so the sale price is £40. A faster equivalent: multiply by (1 minus the rate) for a discount (50 × 0.8 = 40) or (1 plus the rate) to add tax (50 × 1.2 = 60). For sale prices — including stacked discounts — the discount calculator does this in one step.
How do I reverse a percentage to find the original price?
Divide by (1 minus the discount rate) rather than adding the percentage back. If something costs $40 after 20% off, the original was 40 ÷ 0.8 = $50 — not 40 + 20% = $48, which is the most common percentage mistake. The same works in reverse for tax: a $60 total that includes 20% tax was $50 before tax.
What's the difference between a percentage change and percentage points?
If an interest rate moves from 10% to 12%, it rose by 2 percentage points but by 20 percent (2 is one-fifth of 10). News reports often blur the two; use points when both numbers are already percentages and you're describing the gap between them.
What does a percentage over 100 mean?
Nothing is wrong — the part is simply larger than the whole. Going from 50 to 150, for instance, is a 200% increase.
How can I estimate percentages in my head?
Anchor on 10% — just move the decimal point one place. From there, 5% is half of that, 1% is a tenth of it, and 20% is double. For a 15% tip on $64: 10% is $6.40, half again is $3.20, so about $9.60. For quick splits and tips, our tip calculator does this with rounding built in.