How to Calculate Percentage: 10 Everyday Examples — Marks, Salary Hike, Discount, GST and Profit
Percentages show up in marks, salary hikes, discounts, GST and loans. These are the ten formulas you actually need, each with a worked example — and the three mistakes people make most often.
By BizToolsIndia Editorial Team · Published · 4 min read
Key takeaways
- Percentage = (Part ÷ Whole) × 100. Almost every other formula is a rearrangement of this one.
- Percentage change = (New − Old) ÷ Old × 100 — always divide by the old value.
- Two discounts of 20% and 10% make 28% off, not 30%.
- To remove 18% GST from a price, divide by 1.18 — don't subtract 18%.
- A rate going from 5.25% to 5.50% is a rise of 0.25 percentage points, but 4.76%.
The one formula behind them all
Percentage = (Part ÷ Whole) × 100
Part = Whole × Percentage ÷ 100
Whole = Part × 100 ÷ Percentage
If you know any two of part, whole and percentage, you can find the third. The examples below show how each everyday problem fits this pattern.
1–3: The basics
- X% of a number. 18% of ₹2,500 = 2,500 × 18 ÷ 100 = ₹450.
- What percentage one number is of another. 45 out of 60 = 45 ÷ 60 × 100 = 75%.
- Marks percentage. 432 out of 500 = 432 ÷ 500 × 100 = 86.4%. Converting a CGPA instead? Use the CGPA to Percentage Calculator.
4–5: Increase and decrease
Percentage change = (New − Old) ÷ Old × 100
- Salary hike. Salary goes from ₹40,000 to ₹46,000 a month: (46,000 − 40,000) ÷ 40,000 × 100 = 15% hike. See what a hike does to your yearly pay with the Salary Hike Calculator.
- Price drop. A product falls from ₹1,200 to ₹900: (900 − 1,200) ÷ 1,200 × 100 = −25%, a 25% decrease.
Important
6–7: Discounts and reverse percentages
- Two discounts in a row. 20% off, then an extra 10% off ₹2,000: ₹2,000 × 0.80 = ₹1,600, then × 0.90 = ₹1,440 — that's 28% off in total, not 30%. Check any discount with the Discount Calculator.
- Finding the original price. You paid ₹1,600 after 20% off. The original price is ₹1,600 ÷ 0.80 = ₹2,000 — not ₹1,600 + 20% (which would be ₹1,920).
8: GST — adding and removing it
Adding 18% GST to ₹1,000: ₹1,000 × 1.18 = ₹1,180. Removing it from a GST-inclusive ₹1,180: ₹1,180 ÷ 1.18 = ₹1,000. A common mistake is to subtract 18% of ₹1,180 (₹212.40), which gives ₹967.60 — wrong, because the 18% was charged on ₹1,000, not ₹1,180.
Do both directions instantly with the GST Calculator and the Reverse GST Calculator.
9: Profit margin vs markup
You buy at ₹800 and sell at ₹1,000, making ₹200. Measured against cost, that's a 25% markup (200 ÷ 800). Measured against the selling price, it's a 20% margin (200 ÷ 1,000). Mixing them up is one of the most common pricing mistakes in small businesses.
| Markup on cost | Margin on selling price |
|---|---|
| 25% | 20% |
| 50% | 33.3% |
| 100% | 50% |
Work in either direction with the Profit Margin Calculator and the Markup Calculator.
10: Percent vs percentage points
When the RBI raised the repo rate from 5.25% to 5.50%, it rose by 0.25 percentage points — the simple difference. As a percentage change, it rose by 0.25 ÷ 5.25 × 100 = 4.76%. News reports usually mean percentage points (often written as 25 basis points, where 100 basis points = 1 percentage point). Read more in what the October 2026 repo rate hike means for your EMI.
Quick mental shortcuts
- 10%: move the decimal one place left — 10% of ₹4,560 is ₹456.
- 5%: half of 10% — ₹228.
- 1%: move the decimal two places — ₹45.60. Build any percentage from these.
- Swap trick: x% of y = y% of x. 4% of 75 = 75% of 4 = 3.
For anything else — percentage of, percentage change, or what percentage one number is of another — use the Percentage Calculator.
Frequently asked questions
How do I calculate the percentage of marks?
Divide the marks you scored by the maximum marks and multiply by 100. For example, 432 out of 500 is 86.4%.
How do I calculate a percentage increase in salary?
Subtract the old salary from the new one, divide by the old salary and multiply by 100. ₹40,000 to ₹46,000 is a 15% hike.
How do I find the original price before a discount?
Divide the sale price by (1 − discount ÷ 100). ₹1,600 after 20% off was originally ₹1,600 ÷ 0.80 = ₹2,000.
Is a 50% markup the same as a 50% margin?
No. A 50% markup on cost gives a 33.3% margin on the selling price. A 50% margin needs a 100% markup.