In this article
Discounts, exam marks, salary hikes, price rises, interest rates, GST — percentages are everywhere, yet many of us reach for a calculator and still aren’t sure which numbers to divide. The good news: nearly every situation is one of five formulas.
1. Find X% of a number
Result = Number × X ÷ 100
20% of ₹1,500 = 1,500 × 20 ÷ 100 = ₹300.
Mental shortcut: 10% is just moving the decimal point one place left. 10% of ₹1,500 = ₹150, so 20% = ₹300, 5% = ₹75, and 15% = ₹225.
Use it for: discounts, tips, GST on a price, commissions.
2. What percent is one number of another?
Percentage = Part ÷ Whole × 100
You scored 432 out of 500: 432 ÷ 500 × 100 = 86.4%.
Use it for: exam marks, how much of a budget is spent, market share, attendance percentage.
3. Percentage increase or decrease
% change = (New − Old) ÷ Old × 100
Salary rises from ₹40,000 to ₹46,000: (46,000 − 40,000) ÷ 40,000 × 100 = 15% hike.
Petrol goes from ₹100 to ₹95: (95 − 100) ÷ 100 × 100 = 5% decrease.
The key detail: always divide by the old (starting) value. Dividing by the new value is the most common percentage mistake.
4. Add or remove a percentage
To increase a number by a percentage, multiply by (1 + rate):
New value = Old value × (1 + X ÷ 100)
A ₹40,000 salary with a 12% hike becomes 40,000 × 1.12 = ₹44,800.
To reverse an increase — for example, find a price before tax — divide instead:
Original = Final ÷ (1 + X ÷ 100)
If a phone costs ₹23,600 including 18% GST, the price before GST is 23,600 ÷ 1.18 = ₹20,000 — not ₹23,600 minus 18%.
5. Successive percentages
When two percentage changes happen one after another, multiply the factors — don’t add the percentages.
A shirt is 40% off, then an extra 10% off at checkout:
1 × 0.60 × 0.90 = 0.54 → you pay 54% of the price.
Total discount = 46%, not 50%.
This also explains a surprising fact: if an investment falls 50% and then rises 50%, you don’t break even. ₹100 → ₹50 → ₹75. To recover from a 50% fall, you need a 100% gain.
| Fall | Gain needed to recover |
|---|---|
| 10% | 11.1% |
| 25% | 33.3% |
| 50% | 100% |
| 75% | 300% |
Percent vs percentage points
If a home loan rate rises from 8% to 9%, it has risen by 1 percentage point, but by 12.5 percent (1 ÷ 8 × 100). Both statements are true — but they describe different things. Watch for this in news about interest rates, inflation and election results.
Skip the arithmetic
Our Percentage Calculator handles the three most common questions in one place — X% of Y, X as a percentage of Y, and percentage increase or decrease — with the answer updating as you type.
Free toolTry the Percentage CalculatorThree quick percentage calculators in one place.Frequently asked questions
How do I calculate percentage of marks?
Divide marks obtained by total marks and multiply by 100. 432 out of 500 is 432 ÷ 500 × 100 = 86.4%.
How do I reverse a percentage increase?
Divide by (1 + rate). If a price after a 20% increase is ₹600, the original price was 600 ÷ 1.2 = ₹500.
What is the difference between percent and percentage points?
If an interest rate goes from 8% to 10%, it rose by 2 percentage points but by 25 percent. News reports often mix the two up.
Written by the Toolsopedia team. Spotted an error? Tell us and we’ll fix it.