How to calculate percentage: marks, increase and decrease

How to calculate percentage depends on the question you are asking. Three formulas cover almost everything: a percentage of a number, what percent one number is of another (marks), and the percentage change between two values.

1. X% of a number

Result = number × X ÷ 100

18% of ₹2,500 = 2,500 × 18 ÷ 100 = ₹450. For GST on a price, the GST calculator also splits the tax into CGST and SGST.

2. What percent is one number of another (marks)

Percentage = part ÷ total × 100

432 out of 500 = 432 ÷ 500 × 100 = 86.4%. If your mark sheet gives CGPA instead of marks, the conversion depends on your board or university; see the CGPA to percentage formula.

3. Percentage increase or decrease

Change % = (new − old) ÷ old × 100

Always divide by the starting value. That is why equal rises and falls do not cancel. For growth over several years, use CAGR instead.

Percentage points vs percent

If an interest rate goes from 8% to 9%, it rose by 1 percentage point, but by 12.5% of the old rate. News and bank letters use both; check which one is meant.

How to use the percentage calculator

1. Pick the calculator that matches your question: X% of Y, X is what % of Y, or change from X to Y.
2. Type your numbers into the sentence.
3. The answer updates as you type.

For shop offers like “40% + 10% off”, the discount calculator applies the second discount correctly; see how to calculate discount.