Free Percentage Calculator
Calculate any percentage problem instantly. Four modes: find a percentage of a number, calculate what percent X is of Y, compute percentage change, and find values after increase or decrease.
What is 15% of 200?
Result
30
15% of 200
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Frequently Asked Questions
How do I calculate what X% of a number is?+
Multiply the number by the percentage and divide by 100. For example, 15% of 200 = (15 ÷ 100) × 200 = 30. Use the "% of Number" tab and enter the percentage and base number.
How do I calculate what percentage X is of Y?+
Divide X by Y and multiply by 100. For example, 30 out of 200 = (30 ÷ 200) × 100 = 15%. Use the "X is what % of Y" tab.
How is percentage change calculated?+
Percentage change = ((New Value − Old Value) ÷ |Old Value|) × 100. A positive result means an increase; negative means a decrease. For example, from 80 to 100: ((100 − 80) ÷ 80) × 100 = 25% increase.
What is the difference between percentage and percentage points?+
A percentage is a proportion expressed per hundred. Percentage points measure the arithmetic difference between two percentages. If interest rates go from 3% to 5%, that is a 2 percentage point increase, but a 66.7% relative increase. These are often confused in news reporting.
How do I calculate a tip?+
Multiply the bill total by the tip percentage and divide by 100. For a $45 bill with a 20% tip: (45 × 20) ÷ 100 = $9. Use the "% of Number" tab: enter 20 as the percentage and 45 as the number.
How do I calculate a discount?+
To find the final price after a discount: Final Price = Original Price × (1 − Discount% ÷ 100). For a $120 item with a 25% discount: $120 × 0.75 = $90. Use the "Increase/Decrease" tab and enter the original price and discount percentage.
What is reverse percentage?+
Reverse percentage finds the original value before a percentage was applied. If a product costs $90 after a 25% discount, the original price is $90 ÷ 0.75 = $120. Use the "Increase/Decrease" tab — enter the result and the percentage to back-calculate the starting value.
How Percentages Work — And Why They Trip People Up
Percentages are one of the most universally useful calculations in everyday life — and also one of the most consistently misunderstood. The word "percent" means "per hundred," so 45% simply means 45 out of every 100. But when percentages are applied in different directions (finding a part, finding the whole, comparing change), the math changes — and that is where mistakes happen. This calculator handles all four common percentage problems so you never have to remember which formula applies.
Percentage of a number: the most common calculation
"What is 15% of 200?" is the classic percentage calculation. The formula is straightforward: divide the percentage by 100 and multiply by the base number. 15 ÷ 100 × 200 = 30. This applies directly to tips (what is 20% of my $47 bill?), discounts (a 30% off $89 item costs how much?), commissions (what is 8.5% of $12,500 in sales?), and tax calculations. Use the Sales Tax Calculator if you need to compute tax on a purchase with state-specific rates.
Percentage change: the formula that catches people off guard
Percentage change = ((New − Old) ÷ |Old|) × 100. The trap is the denominator: you always divide by the original (old) value, not the new one. A stock that goes from $80 to $100 is a 25% increase (not 20%). If it then falls back from $100 to $80, that is a 20% decrease. The same $20 move represents different percentage changes because the base is different. This asymmetry is why a 50% gain followed by a 50% loss leaves you down 25%, not flat. If you are tracking business metrics or comparing revenue changes, also see the Profit Margin Calculator.
Percentage vs. percentage points: a critical distinction
If a mortgage rate rises from 3% to 5%, news reports often say rates "increased by 2 percentage points." That is different from saying rates increased by 67% (the relative change). Percentage points describe absolute arithmetic differences between two percentages. Relative percentage change describes how large that difference is relative to the starting value. In finance, politics, and healthcare reporting, these two measures are routinely confused — and the difference can be massive. When someone says "our conversion rate improved by 50%," they might mean it went from 2% to 3% (1 percentage point increase, 50% relative increase).
Reverse percentage: working backwards from a result
Reverse percentage answers "what was the original value before the percentage was applied?" If a hotel room costs $135 after a 10% discount, the original price is $135 ÷ 0.90 = $150. This is different from adding 10% to $135 ($148.50). Use the Increase/Decrease tab in reverse: enter the final amount as the base and the percentage to find how the numbers work out. For sales tax reversal — finding the pre-tax price from a tax-inclusive amount — the Sales Tax Calculator has a dedicated reverse mode for all 50 US states.