Twelve calculation types: percent of a value, increase, discount, change, original value, successive discounts, margin and markup, tip, list shares and compound growth.
A percentage is a fraction of 100: 20% is 20 per 100, or 0.20. This calculator gathers twelve problems people actually look for: how much is X% of a value, X is what % of Y, increase and final value, discount and final price, percent change between two values, the original value before a discount or increase, successive discounts (20% and then 10% is not 30%), percentage points, margin and markup, tips with a split bill, each item's share of a list, and a repeated change over several periods. Every mode has a clickable example, shows the formula and the step by step with your own numbers, and lets you copy each result. The math uses exact numbers (fractions), with no floating point noise like 0.30000000000000004, and rounds only when displaying, with the decimal places and rounding mode you choose.
The starting point is 10%: just divide the value by 10. Almost everything comes from it. 1% is the value divided by 100, 5% is half of 10%, 20% is double 10%, 50% is half the value, 25% is a quarter and 75% is three quarters. For 15% of 80, work out 10% (8), add 5% (4) and get 12. For 35% of 200, add 30% (60) and 5% (10) to get 70.
When the numbers get awkward, swap them. X% of Y equals Y% of X, so 8% of 50 is the same as 50% of 8, which is an easy 4. The calculator confirms the result and shows the exact step by step.
Percentages do not add up when one applies to the result of the other. A 20% discount and then 10% multiplies the value by 0.8 and by 0.9, which is 0.72: the total discount is 28%, not 30%. On $250 the price falls to $180. Likewise, raising 25% and then cutting 20% returns exactly the starting value (1.25 × 0.8 = 1), but cutting 50% and raising 50% leaves you 25% below (0.5 × 1.5 = 0.75).
To get back to the earlier value, divide by the factor instead of subtracting the percentage. If you paid $80 after 20% off, the original price was 80 ÷ 0.8 = $100. Removing 20% from 80 would give 64 and adding 20% to 80 would give 96, both wrong. And do not mix up percentage points and percent: a rate of 10% that goes to 12% rose 2 percentage points, which is 20% in relative terms.
Margin and markup measure the same profit on different bases. Margin divides the profit by the selling price, markup divides it by the cost. With a cost of $70 and a price of $100 the profit is $30: the margin is 30% and the markup is 42.86%. The conversion is markup = margin ÷ (1 − margin) and margin = markup ÷ (1 + markup). A 100% markup equals a 50% margin. The calculator converts both ways and starts from what you already know: cost and price, cost and margin, cost and markup, price and margin, or price and markup. Taxes, commissions and shipping are not part of the calculation.
For tips, a $200 bill with 10% becomes $220 and, split by 4, $55 each. If the split is not exact, turn on rounding up: everyone pays a round amount and the surplus is shown separately. In repeated change, the same percentage applies period after period to a value that has already changed: $1,000 at 10% for 3 periods becomes $1,331 (not $1,300), and the table shows every period.
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<iframe
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width="100%"
height="600"
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title="Percentage Calculator"
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<a href="https://jkit.tools/en/tools/percentage-calculator">Percentage Calculator</a>
These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.
Start with 10%, which is the value divided by 10, and build the rest from it: 1% is dividing by 100, 5% is half of 10%, 20% is double 10%, 25% is dividing by 4 and 50% is dividing by 2. For 15% of 80, take 10% (8) plus 5% (4), which is 12. For 35% of 200, add 30% (60) and 5% (10), which is 70. If the numbers are awkward, swap the order: 8% of 50 equals 50% of 8, which is 4.
Find how much a percentage of a value is.
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