Percentages show up in discounts, marks, interest, tax and salary hikes. Almost every case is one of five small formulas. Learn them once, and a calculator is only a way to check your work.
1. Percentage of a number
Result = number × percent ÷ 100
What is 15% of 840? 840 × 15 ÷ 100 = 126.
2. What percent is one number of another?
Percent = part ÷ whole × 100
You scored 412 out of 500. 412 ÷ 500 × 100 = 82.4%.
3. Percentage increase and decrease
Change % = (new − old) ÷ old × 100
A salary rises from ₹40,000 to ₹46,000: (46,000 − 40,000) ÷ 40,000 × 100 = 15% increase. A positive result is an increase, a negative one a decrease.
4. Discounts
Discount amount = price × discount % ÷ 100 Sale price = price − discount amount
A ₹2,499 shirt at 30% off: discount = 749.70, sale price = ₹1,749.30. For two discounts such as “20% plus extra 10%”, apply them one after the other: ×0.80 × 0.90 = ×0.72, which is 28% off, not 30%. The Discount Calculator handles stacked discounts and tax.
5. Finding the original number
Original = final value ÷ (1 ± percent ÷ 100)
A price after a 20% discount is ₹800, so the original was 800 ÷ 0.80 = ₹1,000. If ₹1,180 includes 18% GST, the base was 1,180 ÷ 1.18 = ₹1,000. See the GST guide for that case.
Percentage points versus percent
If an interest rate moves from 8% to 9%, it rose by 1 percentage point but by 12.5 percent (1 ÷ 8). Headlines often mix the two, so check which is meant.
Frequently asked questions
How do I calculate 10% quickly?
Move the decimal point one place left: 10% of 460 is 46. Then build others from it: 5% is half, 20% is double, 15% is 10% plus 5%.
How do I turn a fraction into a percentage?
Divide the top by the bottom and multiply by 100. For 3/8: 3 ÷ 8 = 0.375, so 37.5%.