A free, instant percentage calculator that runs entirely in your browser. Answer the four most common percentage questions in one place: what is X% of a number, what percent one number is of another, the percentage increase or decrease between two values, and what a number becomes after adding or subtracting a percentage. Results update live as you type, with a plain-English restatement so you can sanity-check the math. Nothing is uploaded — it is pure client-side arithmetic.
How to find what X% of a number is
Divide the percentage by 100, then multiply by the number: (X ÷ 100) × Y. For example, 15% of 200 is (15 ÷ 100) × 200 = 30. This is the mode to use for tips, discounts, and tax: a 15% tip on a $200 bill is $30, and a 20% discount on an $80 item saves you $16.
How to work out what percent one number is of another
Divide the part by the whole, then multiply by 100: (X ÷ Y) × 100. For example, 30 out of 200 is (30 ÷ 200) × 100 = 15%. Use this for test scores (42 correct out of 50 = 84%), progress toward a goal, or market share.
How to calculate percentage increase or decrease
Subtract the starting value from the ending value, divide by the starting value, then multiply by 100: ((Y − X) ÷ X) × 100. Going from 200 to 250 is ((250 − 200) ÷ 200) × 100 = a 25% increase; going from 250 to 200 is a 20% decrease. Note the asymmetry — the base changes, which is why a 25% gain and a 20% loss can cancel out. This is the standard way to describe price changes, traffic growth, and year-over-year comparisons.
How to add or subtract a percentage
Multiply the number by (1 + X ÷ 100) to increase it, or (1 − X ÷ 100) to decrease it. For example, 200 increased by 10% is 200 × 1.10 = 220, and 200 decreased by 10% is 200 × 0.90 = 180. Handy for adding sales tax or VAT to a price, applying a raise, or taking a discount off a list price.
Percentage formulas explained
Every percentage problem reduces to one identity: percent = part ÷ whole × 100. The four calculator modes are just that identity solved for a different unknown:
- What is X% of Y? — solving for the part: part = (X ÷ 100) × Y
- X is what % of Y? — solving for the percent: percent = (X ÷ Y) × 100
- Percentage change — the part is the difference: change% = ((new − old) ÷ old) × 100
- Add / subtract a percentage — scaling the whole: result = Y × (1 ± X ÷ 100)
Two things trip people up. First, percentage change always uses the original value as the base. Second, reversing a change doesn't use the same percentage: adding 25% and then subtracting 25% leaves you at 93.75% of where you started, not 100%.
Frequently asked questions
How do I find X% of a number?
Divide the percentage by 100 and multiply by the number. For example, 15% of 200 = (15 ÷ 100) × 200 = 30. Or use the first tab of the calculator above and the result appears as you type.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, and multiply by 100: ((new − old) ÷ old) × 100. Going from 200 to 250 is a 25% increase. If the result is negative, it's a percentage decrease.
What is the difference between percent and percentage points?
Percent is relative; percentage points are absolute. If a rate rises from 10% to 15%, it went up 5 percentage points but 50 percent (because 5 is half of 10). News about interest rates or poll numbers usually means percentage points; growth claims usually mean percent — mixing them up is one of the most common statistics mistakes.
Is this percentage calculator free?
Yes — completely free, no signup, no limits. All four modes run entirely in your browser with plain client-side arithmetic, so nothing you type is ever sent to a server.
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