Percentage Increase & Decrease Calculator
Percent of a number, change, discounts
Percentage change
(100 − 80) ÷ 80 × 100 = 25
+25% increase
Percentage difference
|10 − 15| ÷ ((10 + 15) ÷ 2) × 100 = 40
40%
Value before the change
120 ÷ (1 + 20 ÷ 100) = 100
100
Formula: part = whole × percent ÷ 100 · Updated Oct 22, 2026
Type an old and a new value to get the percentage increase or decrease. Two more boxes give the percentage difference between two values and the value before a percentage change.
How to use the Percentage Increase Calculator
- Enter the old value and the new value.
- The change shows as + (increase) or − (decrease), with the working underneath.
- Use percentage difference when neither value is the "old" one, and value before the change to undo a rise or a cut.
Percentage change formula
(new − old) ÷ |old| × 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = +25%; from 100 to 80 is -20%. The same gap is a different percentage depending on the starting point.
Percentage difference formula
|a − b| ÷ ((a + b) ÷ 2) × 100. It compares two values on an equal footing: 10 and 15 differ by 40%, whichever comes first.
Why +10% then −10% is not zero
100 + 10% = 110, and 110 − 10% = 99. The second change is taken from a bigger number. To undo a rise of P%, divide by (1 + P ÷ 100): after a 20% rise to 120, the original was 120 ÷ 1.2 = 100.
Related guides
Frequently asked questions
How do I calculate percentage increase?
Subtract the old value from the new one, divide by the old value and multiply by 100. 50 → 65 is 30%.
What is the difference between percent change and percentage difference?
Percent change has a direction (old → new) and divides by the old value. Percentage difference has no direction and divides by the average of the two.
What is a percentage point?
The plain difference between two percentages. A rate going from 4% to 5% rose by 1 percentage point, which is a 25% increase.
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Results are rounded for display; the calculation itself uses full precision. Tax and price results are estimates — check the official rate for your case.