Percentages show up everywhere in daily life in India — your exam marksheet, the GST on a restaurant bill, a "Flat 40% Off" sale banner, your annual salary hike letter, cricket batting averages, and your mutual fund returns statement all speak the language of percentages. Yet many people still find percentage calculations confusing, especially percentage increase vs decrease, or profit margin vs markup.
This guide covers every percentage formula you'll actually need, with over 50 solved real-life examples using Indian numbers — school marks, GST invoices, shopping discounts, salary hikes, investments, cricket stats, and business profit — so you can calculate any percentage confidently, with or without a calculator.
What Is Percentage?
A percentage is simply a way of expressing a number as a fraction of 100. The word itself comes from the Latin "per centum," meaning "per hundred." So when we say 45%, we mean 45 out of every 100 — or 0.45 as a decimal, or 45/100 as a fraction. Percentages make it easy to compare quantities of different sizes on a single, standardized scale.
Percentage Formula
The core formula behind almost every percentage calculation is:
Percentage = (Part ÷ Whole) × 100
Everything else in this guide — increase, decrease, marks, GST, discount, profit, salary hikes — is a variation of this one basic idea.
How to Calculate Percentage (Step by Step)
- Identify the "part" (the specific number you're interested in) and the "whole" (the total or base number)
- Divide the part by the whole to get a decimal
- Multiply the result by 100 to convert it into a percentage
Example: You scored 72 marks out of 90. Percentage = (72 ÷ 90) × 100 = 0.8 × 100 = 80%.
For instant results without manual calculation, try CalcMitra's Percentage Calculator.
Percentage Increase Formula
Percentage Increase = ((New Value − Old Value) ÷ Old Value) × 100
Example: Your monthly grocery bill rose from ₹6,000 to ₹6,900. Increase = ((6,900 − 6,000) ÷ 6,000) × 100 = 15%.
Percentage Decrease Formula
Percentage Decrease = ((Old Value − New Value) ÷ Old Value) × 100
Example: A smartphone's price dropped from ₹25,000 to ₹19,500. Decrease = ((25,000 − 19,500) ÷ 25,000) × 100 = 22%.
Percentage of Marks
For exam results: Percentage = (Marks Obtained ÷ Maximum Marks) × 100. If subjects have different maximum marks, add up all marks obtained and all maximum marks first, then apply the formula once to the totals — not subject by subject.
Example: A student scores 432 out of 500 in Class 10 board exams. Percentage = (432 ÷ 500) × 100 = 86.4%.
GST Percentage
GST Amount = (Taxable Value × GST Rate) ÷ 100 and Total Invoice = Taxable Value + GST Amount. To reverse-calculate the base price from a GST-inclusive total: Base Price = Total ÷ (1 + GST Rate/100).
Example: A restaurant bill of ₹2,400 (before GST) with 5% GST = (2,400 × 5) ÷ 100 = ₹120 GST, so the final bill is ₹2,520. For a full walkthrough of India's GST slabs and input tax credit, see our GST Calculation Guide, or use the GST Calculator directly.
Discount Percentage
Discount Amount = (MRP × Discount%) ÷ 100 and Final Price = MRP − Discount Amount.
Example: A "Flat 40% Off" jacket with MRP ₹3,500: Discount = (3,500 × 40) ÷ 100 = ₹1,400, so you pay ₹2,100. Try the Discount Calculator to check any sale offer instantly, including stacked discounts (e.g., "40% + extra 10%" — which is not the same as a flat 50% off).
Profit Margin Percentage
Two related but different formulas trip up most people:
- Profit Margin % = (Profit ÷ Selling Price) × 100 — profit as a share of what the customer paid
- Markup % = (Profit ÷ Cost Price) × 100 — profit as a share of what it cost you
Example: A shopkeeper buys a shirt for ₹800 (Cost Price) and sells it for ₹1,000 (Selling Price). Profit = ₹200. Margin = (200 ÷ 1,000) × 100 = 20%. Markup = (200 ÷ 800) × 100 = 25%. Use the Profit Margin Calculator to avoid mixing these up when pricing your own products.
Salary Increment Percentage
Salary Hike % = ((New CTC − Old CTC) ÷ Old CTC) × 100.
Example: Your appraisal letter shows CTC moving from ₹6,50,000 to ₹7,54,000. Hike = ((7,54,000 − 6,50,000) ÷ 6,50,000) × 100 = 16%. Use the Salary Calculator to also see how a CTC hike translates to your monthly in-hand salary after deductions.
Commission Percentage
Commission = (Sales Amount × Commission Rate) ÷ 100.
Example: A real estate agent earns 2% commission on a ₹75,00,000 property sale: Commission = (75,00,000 × 2) ÷ 100 = ₹1,50,000.
Interest Percentage
Simple Interest = (Principal × Rate × Time) ÷ 100.
Example: ₹1,00,000 invested at 7% simple interest for 3 years earns (1,00,000 × 7 × 3) ÷ 100 = ₹21,000 interest. For compounding investments like SIPs, growth isn't linear — see our Mutual Fund SIP Guide to understand how percentage returns compound over time, or try the SIP Calculator.
Percentage Change (General)
Percentage Change = ((New Value − Old Value) ÷ Old Value) × 100 — positive for an increase, negative for a decrease. This single formula covers both increase and decrease; the sign of the result tells you the direction.
Important distinction: "Percentage change" (relative) is not the same as "percentage points" (absolute difference). If your savings rate goes from 20% of income to 25% of income, that's a 5 percentage point increase, but a 25% relative increase in your savings rate — both are correct, but they answer different questions.
Reverse Percentage: Finding the Original Value
Sometimes you know the final value and the percentage applied, but need to find the original number — this is called a reverse percentage calculation, and it trips up even people who are comfortable with normal percentage math.
Original Value = Final Value ÷ (1 ± Percentage/100) (use "+" if the final value includes an increase, "−" if it includes a decrease)
Example: After a 12% price hike, a product now costs ₹560. What was the original price? Original = 560 ÷ 1.12 = ₹500. This is exactly how GST-inclusive prices are reverse-calculated to find the base taxable value, and how a "final salary after 15% hike" figure can be worked backward to the original CTC.
Successive Percentage Changes (Compounding)
One of the most common percentage mistakes is assuming that two successive percentage changes simply add up. They don't — because the second change applies to the already-changed value, not the original one.
Example: A stock price rises 20% in one month, then falls 20% the next month. Does it return to the original price? No — starting at ₹1,000: after a 20% rise it becomes ₹1,200; after a 20% fall on ₹1,200, it drops by ₹240 to ₹960, not back to ₹1,000. This is why equal-but-opposite percentage swings never cancel out perfectly, and why "successive discounts" (like the 40%+10% example earlier) never simply add together.
For two successive percentage changes of a% and b%, the combined effect is: Combined % = a + b + (a × b ÷ 100). Using the stock example: a = +20, b = −20, so Combined % = 20 + (−20) + (20 × −20 ÷ 100) = 0 − 4 = −4%, matching the ₹960 result exactly.
50+ Solved Percentage Examples
Below are real-life percentage calculations grouped by category, so you can find an example close to your own situation.
School & Exam Marks
| Marks Obtained | Total Marks | Percentage |
|---|---|---|
| 432 | 500 | 86.4% |
| 78 | 100 | 78% |
| 560 | 600 | 93.33% |
| 29 | 50 | 58% |
| 341 | 450 | 75.78% |
| 18 | 25 | 72% |
| 489 | 500 | 97.8% |
| 210 | 300 | 70% |
| 37 | 40 | 92.5% |
| 396 | 500 | 79.2% |
GST Invoices
| Taxable Value | GST Rate | GST Amount | Total Invoice |
|---|---|---|---|
| ₹2,400 | 5% | ₹120 | ₹2,520 |
| ₹10,000 | 12% | ₹1,200 | ₹11,200 |
| ₹5,000 | 18% | ₹900 | ₹5,900 |
| ₹1,20,000 | 28% | ₹33,600 | ₹1,53,600 |
| ₹850 | 5% | ₹42.50 | ₹892.50 |
| ₹45,000 | 18% | ₹8,100 | ₹53,100 |
| ₹3,20,000 | 12% | ₹38,400 | ₹3,58,400 |
Shopping Discounts
| MRP | Discount % | You Save | Final Price |
|---|---|---|---|
| ₹3,500 | 40% | ₹1,400 | ₹2,100 |
| ₹1,200 | 25% | ₹300 | ₹900 |
| ₹60,000 | 10% | ₹6,000 | ₹54,000 |
| ₹899 | 30% | ₹269.70 | ₹629.30 |
| ₹15,000 | 50% | ₹7,500 | ₹7,500 |
| ₹2,499 | 20% | ₹499.80 | ₹1,999.20 |
Callout: "40% + extra 10%" is not a flat 50% off. It's applied in two steps: first 40% off, then 10% off the already-discounted price — giving a combined discount of only 46%, not 50%.
Business Profit & Loss
| Cost Price | Selling Price | Profit/Loss | Profit/Loss % |
|---|---|---|---|
| ₹800 | ₹1,000 | ₹200 profit | 25% (markup) |
| ₹5,00,000 | ₹4,60,000 | ₹40,000 loss | 8% loss |
| ₹1,20,000 | ₹1,50,000 | ₹30,000 profit | 25% (markup) |
| ₹45 | ₹60 | ₹15 profit | 33.33% (markup) |
| ₹8,00,000 | ₹9,60,000 | ₹1,60,000 profit | 20% (markup) |
| ₹250 | ₹200 | ₹50 loss | 20% loss |
Salary Hikes
| Old CTC | New CTC | Hike % |
|---|---|---|
| ₹6,50,000 | ₹7,54,000 | 16% |
| ₹4,00,000 | ₹4,60,000 | 15% |
| ₹12,00,000 | ₹14,40,000 | 20% |
| ₹8,00,000 | ₹8,64,000 | 8% |
| ₹3,00,000 | ₹3,90,000 | 30% |
Investments & Returns
| Invested | Current Value | Return % |
|---|---|---|
| ₹10,000 | ₹25,000 | 150% |
| ₹5,00,000 | ₹6,10,000 | 22% |
| ₹1,00,000 | ₹1,12,000 | 12% |
| ₹2,50,000 | ₹2,15,000 | -14% (loss) |
| ₹75,000 | ₹97,500 | 30% |
Cricket Statistics
| Stat | Values | Percentage |
|---|---|---|
| Boundary % (runs from boundaries) | 48 of 80 runs | 60% |
| Strike rate (runs per 100 balls) | 65 runs off 50 balls | 130 (i.e., 130%) |
| Team win percentage | 27 wins in 40 matches | 67.5% |
| Catches taken | 18 of 25 chances | 72% |
| Bowling economy improvement | 6.0 to 4.8 runs/over | 20% decrease |
Commission & Interest
| Scenario | Rate | Result |
|---|---|---|
| Real estate commission on ₹75,00,000 sale | 2% | ₹1,50,000 |
| Insurance agent commission on ₹40,000 premium | 15% | ₹6,000 |
| Simple interest on ₹1,00,000 for 3 years | 7% | ₹21,000 |
| Simple interest on ₹2,50,000 for 2 years | 8.5% | ₹42,500 |
| Tip on a ₹1,800 restaurant bill | 10% | ₹180 |
| Income tax on ₹12,00,000 slab portion | 15% | ₹1,80,000 on that slab |
That's 50+ worked examples across marks, GST, discounts, profit, salary, investments, cricket, and commission/interest — for tax-specific calculations, see our Income Tax Guide, and for building these numbers into a broader money plan, see our Financial Planning Guide.
Common Mistakes
- Dividing by the new value instead of the old value when calculating percentage increase/decrease — always divide by the original number
- Confusing percentage points with percentage change — a rate moving from 12% to 18% is 6 percentage points, but a 50% relative increase
- Adding two percentages directly for successive discounts — "40% + 10%" is not 50% off; it's 46% off, since the second discount applies to the already-reduced price
- Mixing up markup and margin — markup is profit over cost price, margin is profit over selling price; they give different numbers for the same transaction
- Forgetting to convert the percentage to a decimal (divide by 100) before multiplying in multi-step calculations
- Comparing CTC hike to in-hand salary hike as if they're the same — CTC includes components that don't always show up in take-home pay
Quick Tricks
- 10% trick: Move the decimal point one place to the left. 10% of ₹4,500 = ₹450.
- 5% trick: Find 10% first, then halve it. 5% of ₹4,500 = ₹225.
- 1% trick: Move the decimal point two places to the left. 1% of ₹4,500 = ₹45.
- Swap trick: x% of y = y% of x. So 8% of 50 is hard to picture, but 50% of 8 = 4 gives you the same answer instantly.
- Combining multiples: Build any percentage from 10% and 1% blocks — e.g., 23% = (10% × 2) + (1% × 3), so 23% of ₹4,500 = ₹900 + ₹135 = ₹1,035.
- Halving and doubling: To find 25%, halve twice (halve for 50%, then halve again). To find 75%, find 25% and subtract it from the full amount, or find 50% + 25%.
- Quick tip estimator: For a restaurant bill, 10% is a base tip, 15% is generous, and 20% is very generous — all derivable from the 10% trick by adding half again for 15%, or doubling for 20%.
- Sanity-check your answer: A percentage of a positive number should always feel proportionate — if your "10%" answer looks bigger than half the original number, you've likely made a decimal-place error worth rechecking.
Conclusion
Once you internalize the single core formula — Percentage = (Part ÷ Whole) × 100 — every other percentage calculation you'll ever need in real life, from exam results to GST bills to salary hikes, is just a variation of it. Practice with the 50+ examples above using your own numbers, and use the quick tricks for fast mental math when you don't have a calculator handy.
Try CalcMitra's Percentage Calculator for instant and accurate percentage calculations.