Percentage calculator
Five percentage problems in one page: percent of a value, what percent, percent change, discount and markup, and proportional splitting — all results copyable.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
30What this tool does
- Stop doing percentage arithmetic in your head: work out X% of Y, what percent X is of Y, and the change from 100 to 150 in one go.
- Handle pricing: give the original price and a discount rate to get the final price and the amount saved, or switch to markup mode to price from cost.
- Split money without losing a cent: proportional allocation uses the largest-remainder method, rounding to the smallest unit first and distributing the leftover to the largest fractions, so the parts always add up to the total.
- Get cent-accurate results: every formula is arranged as multiply-then-divide with a decimal rounding nudge, so boundaries like 1.005 do not come out a cent short because of binary float error.
Example
Input
Mode: discount / markup Original price: 200 Rate: 25
Output
Final price: 150 Saved: 50
Switching the same numbers to markup gives a final price of 250 with 50 added. In split-by-ratio mode a total of 100 with weights 1, 2, 3 yields 16.67, 33.33 and 50, which sums to exactly 100.
Frequently asked questions
Does "percent change from X to Y" report a percentage or a difference?
Both. The percentage is (Y − X) ÷ X × 100 with a negative sign when it falls, and the second line gives the absolute difference Y − X, so you can keep "up 50%" and "up 50 units" apart at a glance.
How do discount and markup differ?
A discount moves the original price down: final = original × (100 − rate) ÷ 100. A markup adds to the cost: final = cost × (100 + rate) ÷ 100. The formulas differ, so pick the direction with the toggle at the top of the pricing mode.
Why does the proportional split never come out a cent short?
It uses the largest-remainder method: each share is floored to the smallest unit, then the leftover units are handed out in order of the largest fractional part. The parts therefore sum to exactly the total, unlike rounding each line on its own.
Can weights be negative or zero?
Weights cannot be negative (you get "weights cannot be negative") and a zero weight simply receives nothing, but the weights must not add up to zero. They may be separated by commas, spaces, newlines or ideographic commas, so pasting "1, 2, 3" works.
How many decimal places are shown?
Display keeps at most 6 decimals and trims trailing zeros, while the money-oriented modes (discount, allocation) compute at 2 decimals. Do further exact arithmetic locally rather than chaining operations on a rounded display value.
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