Percentage Calculator
Find a percentage of a number, calculate a percentage change, add a percentage, or reverse an included percentage.
Percentage Calculator
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Guide updated 6 October 2026
Calculate a percentage of a number, compare two values, add a percentage increase or recover the value before an included increase. The calculator shows the result and the arithmetic used. Choosing the right mode matters more than remembering a single percentage formula.
How to use the percentage calculator
- Choose the operation that matches your question.
- Read what A and B represent in that mode.
- Enter both values and select Calculate.
- Check the displayed formula, units and reference value.
A percentage means parts per hundred. In “A percent of B,” A is the rate and B is the amount. In the increase mode, A is the starting amount and B is the rate. Those positions are intentionally different.
Percentage formulas for the four modes
| Question | Formula used | Example |
|---|---|---|
| A percent of B | A × B ÷ 100 | 12% of 250 = 30 |
| Change from A to B | (B − A) ÷ |A| × 100 | 80 to 92 = +15% |
| Increase A by B percent | A × (1 + B ÷ 100) | 250 plus 12% = 280 |
| Remove an included B percent increase from A | A ÷ (1 + B ÷ 100) | 280 before a 12% increase = 250 |
The absolute value in the change denominator matters for negative starting values. For ordinary positive prices and measurements, it produces the usual percentage-change calculation.
Percentage increase and decrease between two values
The starting value is the reference. Moving from 40 to 60 is a 50% increase; moving back from 60 to 40 is a 33.333333% decrease. The absolute difference is 20 in both directions, but the bases differ.
A starting value of zero makes relative percentage change undefined. Use the absolute difference instead. Negative starting values need context: the number shown is arithmetic relative to the absolute base, not a judgment that a financial result has improved.
Calculate a discount without confusing it with reversal
To subtract 15% from a price of 80, choose the increase mode with A = 80 and B = −15. The result is 68. Alternatively, calculate 15% of 80 to get the discount amount, 12, and subtract it yourself.
Removing an increase already included in a total is a different operation. If 120 includes a 20% increase, the original was 120 ÷ 1.20 = 100. Subtracting 20% of 120 gives 96 and does not undo that increase.
Percentages versus percentage points
When a rate changes from 4% to 6%, the difference is two percentage points. Its relative increase is 50%, because (6 − 4) ÷ 4 × 100 = 50. State which measure you mean when comparing rates.
If you need to find what percentage a part represents of a whole, divide the part by the whole and multiply by 100. That separate operation is not one of this version’s four dropdown modes.
Common errors and result precision
Check the order of A and B, the selected mode and whether your input is a whole amount or already a percentage. Results are rounded to up to six decimal places for display. The reverse mode cannot use a rate of −100%, because its denominator becomes zero.
The tool applies arithmetic to the inputs you provide. It does not choose a tax rate, interpret a statutory rule or calculate a compound sequence automatically. For successive changes, apply each change to the result of the previous one.
Percentage calculator FAQs
How do I find 12% of 250?
Choose A percent of B, enter A = 12 and B = 250. The answer is 30.
How do I apply a price reduction?
Use the increase mode with a negative rate, such as −15 for a 15% reduction.
Why does adding 20% and subtracting 20% not cancel out?
The second percentage uses a changed base. Use division by 1.20 to reverse a 20% increase.
Can I calculate change from zero?
Not as a defined relative percentage. Report the absolute difference instead.
Are tax rates built into this tool?
No. It uses the rate you enter.