How to calculate a percentage
A percentage is a fraction of 100. To find X% of a number, multiply the number by X and divide by 100. To find what percent one number is of another, divide the first by the second and multiply by 100. For percentage change, take the difference, divide by the original value, and multiply by 100.
Everyday uses
- Marks and exam scores (got 45 out of 180 → what percent).
- Discounts, tips, taxes and interest.
- Salary hikes and price changes (₹800 → ₹1,000 is a 25% rise).
Worked examples
Percentage of a number: 18% of 4,500 is 4,500 × 18 ÷ 100 = 810.
What percent one number is of another: 36 out of 45 is 36 ÷ 45 × 100 = 80%.
Percentage change: a price moving from 250 to 310 is (310 − 250) ÷ 250 × 100 = a 24% increase. Going back from 310 to 250 is a 19.4% decrease — the two are not the same number, because each is measured against a different starting point.
The mistake almost everyone makes
A percentage is meaningless without knowing what it is a percentage of. A 50% rise followed by a 50% fall does not return you to where you started: 100 rises to 150, then falls to 75. The rise was measured against 100 and the fall against 150.
The same trap appears in salary hikes, discount stacking and any figure quoted as a "percentage point" change, which means something different again — a move from 5% to 7% is two percentage points, but a 40% increase.
Frequently asked questions
How do I add a percentage to a number?
Multiply by (1 + percent ÷ 100). For example, ₹2,000 + 15% = 2000 × 1.15 = ₹2,300.
What does percentage change mean?
It shows how much a value grew or fell relative to its starting value — positive for an increase, negative for a decrease.
How do I reverse a percentage increase?
Divide rather than subtract. A number that is 120 after a 20% increase was 120 divided by 1.2, which is 100 — not 120 minus 20%, which would give 96.
What is the difference between percent and percentage points?
Percentage points measure the gap between two percentages directly. Interest moving from 6% to 9% is a rise of three percentage points, but a 50% increase in the rate itself. Both are correct and they describe different things.
How do I calculate a percentage without a calculator?
Find 10% by moving the decimal one place left, then build from there. 10% of 640 is 64, so 5% is 32 and 15% is 96. Most everyday percentages can be assembled from 10%, 5% and 1%.