About this tool
Three percentage calculations in one panel: find X% of a number, find what percentage one number is of another, and find the percentage change between an old and a new value. Each updates live as you type.
Percentage change is the one people get backwards: it is always measured against the original value, so a price going from 50 to 75 is a 50% increase, but falling from 75 back to 50 is only a 33.3% decrease. The asymmetry trips up discount math and investment returns alike.
How to use it
- Pick the calculation that matches your question.
- Enter the two numbers.
- Read the live result — no Calculate button needed.
Frequently asked questions
How do I calculate X% of a number by hand?
Multiply the number by the percentage and divide by 100. 18% of 250 = 250 × 18 ÷ 100 = 45.
If a price drops 20% then rises 20%, am I back where I started?
No — you end 4% below the start. The rise is calculated on the smaller, post-drop base. 100 → 80 → 96.
What is a percentage point?
The absolute difference between two percentages. An interest rate going from 4% to 6% rises two percentage points, but that is a 50% relative increase.