Percentage formulas
X% of Y = X × Y ÷ 100
X as % of Y = X ÷ Y × 100
% change = (New − Old) ÷ Old × 100
X as % of Y = X ÷ Y × 100
% change = (New − Old) ÷ Old × 100
Everyday examples
- Discounts: 20% off ₹1,999 → use "Add / subtract a %" → ₹1,599.20.
- Exam marks: 450 out of 600 → "X is what % of Y" → 75%.
- Salary hike: ₹80,000 to ₹1,00,000 → "Percentage change" → 25% increase.
- Tips & tax: 15% of a ₹2,400 bill → ₹360.
Percentage vs percentage points
If an interest rate goes from 8% to 10%, it rose by 2 percentage points but by 25 percent. Mixing the two up is one of the most common maths mistakes in news headlines.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 15% of 2,400 = 2,400 × 15 ÷ 100 = 360.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, then multiply by 100.
How do I reverse a percentage?
To find the original price before a 20% increase, divide by 1.20. Before a 20% discount, divide by 0.80.