Calculator
Percentage calculator
Eight modes cover a percentage of a number, a share, change and prices before or after a change. Always check which value is the base. An increase followed by the same percentage decrease does not cancel out.
Calculator
Enter data
Choose an operation, then enter A and B as described by the mode. Fields marked with an asterisk are required.
How to use the calculator
- Choose an operation and match the numbers to A and B.
- Inspect the result formula. A percentage is a ratio, not a percentage-point difference.
Calculation details
Formula and calculation method
Percentage of a number: A × B/100. Share: A/B × 100%. Changed price: A × (1 ± B/100); original price: A/(1 ± B/100). Change: (B − A)/|A| × 100%.
Worked example
A price of PLN 120 after a 20% increase means 120 / 1.2 = PLN 100 originally. Reducing PLN 100 by 20% gives PLN 80.
Limitations
- Division by zero is rejected. Reversing a 100% decrease is indeterminate. Prices and price-change rates must be nonnegative; decreases are capped at 100%.
- Change uses the absolute starting base when negative. This is a mathematical convention, not a profitability model.
Sources
Engine version: 2.0 (2026-09-23) · Last reviewed: 23 September 2026
Frequently asked questions
Do +20% and −20% restore the price?
No: 100 × 1.2 × 0.8 = 96. The second percentage uses the changed base.
Is 5% to 7% a 2% increase?
It is 2 percentage points or a 40% relative increase. Change mode calculates the latter.