Result
50
The sum
20% × 250
what was calculated
The rest
200
the other 80%
250 increased by 20%
300
value + percentage
250 decreased by 20%
200
value − percentage
How the Percentage Calculator Works
Percentage of a number
Multiply and divide by a hundred: result = value × percent ÷ 100. So 20% of 250 is 250 × 20 ÷ 100 = 50. The shortcut worth internalising is that 10% is just the number with its decimal point moved one place left — everything else builds from there.
Percentage change vs percentage difference
These are not the same thing and the distinction matters. Percentage change has a direction — it measures a move from an old value to a new one, (new − old) ÷ old × 100 — so swapping the inputs gives a different answer. Percentage difference compares two values against their average, |a − b| ÷ ((a + b) ÷ 2) × 100, and is symmetric. Use change for before-and-after; use difference when neither value is the baseline.
The asymmetry that catches people out
A 50% rise followed by a 50% fall does not return you to where you started. 100 rises to 150, then falls to 75 — because the fall is taken from the larger number. The same arithmetic is why an investment that drops 50% must gain 100% to break even. Percentages are always relative to whatever base they are applied to.
Percent versus percentage point
If a rate moves from 4% to 5%, that is a rise of one percentage point but a 25% relative increase. Both are correct, and quoting whichever sounds more dramatic is a favourite trick of misleading statistics.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 20% of 250 is 250 × 20 ÷ 100 = 50. A useful shortcut: 10% is the number with the decimal point moved one place left, so 20% is just double that.
How do I work out percentage change?
Subtract the old value from the new one, divide by the old value, and multiply by 100: change = (new − old) ÷ old × 100. Going from 250 to 300 is (300 − 250) ÷ 250 × 100 = a 20% increase. A negative result means a decrease.
What is the difference between percentage change and percentage difference?
Percentage change has a direction — it measures the move from a starting value to an ending one, so it is not symmetric. Percentage difference compares two values relative to their average and has no direction, so it gives the same answer whichever order you enter them. Use change for before-and-after, and difference for comparing two independent measurements.
Why can't I calculate percentage change from zero?
Because any increase from zero is infinite in percentage terms. Going from 0 to 50 is not a 50% or 5000% increase — dividing by zero has no answer. When the starting value is zero, report the absolute change instead.
Why is a 50% rise then a 50% fall not back where I started?
Because each percentage applies to a different base. 100 rising 50% is 150; 150 falling 50% is 75, not 100. The fall is taken from the larger number, so it removes more. This is the same reason a stock that drops 50% needs to gain 100% to recover.
What is a percentage point?
A percentage point is the plain arithmetic gap between two percentages, while a percent change is relative. If a rate goes from 4% to 5%, that is a rise of one percentage point but a 25% increase. Mixing the two up is a common source of misleading statistics.