Percentage Calculator
Three-mode percentage calculator: X% of Y, X is what % of Y, and percentage change.
What is X% of Y?
?
X is what % of Y?
?
% Change from X to Y
?
The three calculations and their formulas
A percentage is a ratio expressed per hundred, so every percentage question reduces to one of three arrangements of the same equation. Finding a part uses part = percentage divided by one hundred, multiplied by the whole, which answers questions such as the tax on a purchase or a tip on a bill. Finding a rate uses percentage = part divided by whole, multiplied by one hundred, which answers what share one figure represents of another. Finding a change uses percentage change = the difference between new and old, divided by the old value, multiplied by one hundred, which is the correct form for growth, discount and variance reporting.
Percentage change versus percentage points
A frequent reporting error is to confuse a relative change with an absolute one. If an interest rate moves from four percent to five percent, that is a rise of one percentage point but a relative increase of twenty-five percent. Both statements are true and they are not interchangeable, so financial and statistical writing distinguishes them explicitly. A second common trap is that successive percentage changes do not add: a fifty percent fall followed by a fifty percent rise leaves you at seventy-five percent of the starting value, because the second change is applied to the smaller base.
Reversing a percentage
To recover an original amount from a total that already includes a markup or a tax, divide rather than subtract: a price of 120 that includes twenty percent tax has a base of 120 divided by 1.2, which is 100, not 120 minus twenty percent, which would be 96. The same reversal applies to discounts, where the pre-discount price equals the paid price divided by one minus the discount rate. Compounding follows the multiplicative form, so an amount growing at a fixed rate over several periods is multiplied by one plus the rate raised to the number of periods.
Frequently asked questions
- How do I calculate X percent of a number?
- Divide the percentage by 100 and multiply by the number. 15% of 240 is 0.15 × 240 = 36. Mentally, 10% is the number with the decimal point moved one place left, and 5% is half of that, so 15% of 240 = 24 + 12 = 36.
- How do I work out what percentage one number is of another?
- Divide the part by the whole and multiply by 100. 36 out of 240 is 36 ÷ 240 × 100 = 15%. Keep the order straight: the figure you are measuring goes on top, the total it is measured against goes underneath.
- What is the difference between a percent and a percentage point?
- A percentage point is an absolute difference between two percentages; a percent is a relative one. A rate moving from 4% to 5% rises by 1 percentage point and by 25 percent. Reports that blur the two overstate or understate the change badly.
- How do I remove a percentage that is already included in a total?
- Divide, do not subtract. A total of 120 that includes 20% tax has a base of 120 ÷ 1.20 = 100. Subtracting 20% of 120 gives 96, which is wrong because the 20% was charged on 100, not on 120.
- Why does a 50% loss need a 100% gain to recover?
- Because each change applies to the current value, not the original. Falling 50% from 100 leaves 50; getting back to 100 from 50 is a 100% gain. Successive percentage changes multiply — they never add.
- How do I calculate percentage increase between two values?
- Subtract the old value from the new, divide by the old value, then multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%. A negative result is a decrease.
Cite this page
UnitConvertLab. (2026). Percentage Calculator. UnitConvertLab. Retrieved from https://unitconvertlab.com/tools/percentage-calculator