Percentages are everywhere — exam results, salary negotiations, GST invoices, EMI breakdowns, discount tags, and bank interest rates. Yet a surprising number of people blank out when asked to calculate a percentage quickly or work one backwards from a total that already includes tax.
This guide breaks down every type of percentage calculation with plain-language formulas and real Indian examples. By the end, you will be able to do most of these in your head — and know exactly when to reach for a calculator for the harder ones.
The 6 Core Percentage Formulas
Every percentage problem you will ever encounter falls into one of six types. Here they all are at a glance:
Percentage of a Number — With Examples
This is the most common type. The formula is: Result = (Number × Percentage) ÷ 100.
Worked examples
Your employer deducts 10% TDS on a ₹85,000 freelance payment. How much is deducted?
TDS = (85,000 × 10) ÷ 100
A property costs ₹65,00,000. The bank requires a 20% down payment. How much do you need upfront?
Down payment = (65,00,000 × 20) ÷ 100
You scored 378 marks out of 500 in your Class 12 boards. What is your percentage?
Percentage = (378 ÷ 500) × 100
💡 Mental maths shortcut: To find 10% of any number, just move the decimal point one place left. To find 5%, halve that. To find 15%, add 10% and 5% together. For 1%, move the decimal two places left. These shortcuts handle most everyday calculations in seconds.
Percentage Increase and Decrease
Percentage change tells you by how much something grew or shrank, expressed as a proportion of the original value. The formula is: % Change = ((New Value − Old Value) ÷ Old Value) × 100.
Salary hike example
Your CTC was ₹7,20,000 per year. After appraisal it becomes ₹8,46,000. What is the hike percentage?
% Hike = ((8,46,000 − 7,20,000) ÷ 7,20,000) × 100
= (1,26,000 ÷ 7,20,000) × 100
Price rise example
Petrol was ₹94.72/litre last month. This month it is ₹97.82/litre. What is the percentage increase?
% Increase = ((97.82 − 94.72) ÷ 94.72) × 100
= (3.10 ÷ 94.72) × 100
⚠️ Common confusion: A 50% increase followed by a 50% decrease does NOT bring you back to the original number. If ₹1,000 increases by 50% it becomes ₹1,500. A 50% decrease on ₹1,500 gives ₹750 — not ₹1,000. Percentage changes compound, they do not cancel each other out.
Reverse Percentage (Working Backwards)
Reverse percentage is used when you know the final value after a percentage has been applied, and you need to find the original value before it was applied. This comes up constantly with GST, discounts, and commission calculations.
Formula for reversing an addition (e.g. tax included)
Original = Final Value ÷ (1 + Rate ÷ 100)
A restaurant bill is ₹2,124 including 18% GST. What was the food cost before GST?
Original = 2,124 ÷ (1 + 18 ÷ 100) = 2,124 ÷ 1.18
Formula for reversing a deduction (e.g. discount applied)
Original = Final Value ÷ (1 − Rate ÷ 100)
A shirt is on sale for ₹680 after a 15% discount. What was the original MRP?
Original = 680 ÷ (1 − 15 ÷ 100) = 680 ÷ 0.85
GST Calculation in India — All Slabs Explained
GST (Goods and Services Tax) replaced a complex web of indirect taxes in India from July 2017. It is applied at multiple rates depending on the category of goods or services. Understanding how to calculate GST — in both directions — is essential for business owners, freelancers, and everyday consumers.
India's GST slab rates
| GST Slab | What It Covers | Common Examples |
|---|---|---|
| 0% (Exempt) | Essential goods and services | Fresh vegetables, milk, eggs, healthcare, education |
| 5% | Basic necessities with some processing | Packaged food, tea, coffee, domestic LPG, economy class airfare |
| 12% | Standard goods | Processed foods, computers, mobile phones (some), business class airfare |
| 18% | Most goods and services | Restaurants (AC), financial services, telecom, most consumer goods, software |
| 28% | Luxury and sin goods | Automobiles, large TVs, cigarettes, aerated drinks, casinos |
Adding GST to a price
Reverse GST — finding the pre-tax price from an inclusive total
A freelance invoice shows ₹35,400 as the total including 18% GST. What is the base amount and how much is GST?
Base Amount = 35,400 ÷ 1.18
✅ GST registration threshold: Businesses with annual turnover above ₹40 lakh (₹20 lakh for services, ₹10 lakh for special category states) must register for GST. If you are a freelancer billing clients regularly, track your cumulative annual revenue against these thresholds.
Calculate GST & Percentages Instantly
ToolLoom's Percentage Calculator has dedicated GST modes — add GST, remove GST, or find the base amount from any GST-inclusive total. Free, no signup.
% Open Percentage Calculator →Exam Marks Percentage — CBSE, Boards & Entrance Tests
Calculating percentage from marks is straightforward: % = (Marks Obtained ÷ Total Marks) × 100. But different boards and entrance exams have specific nuances worth knowing.
CBSE Class 10 and Class 12 — best of five rule
CBSE calculates the official Class 10 percentage using the best five subjects out of the ones attempted, with one compulsory language subject always included. This means your overall percentage may differ from a simple average of all subjects. For Class 12, the merit percentage for most universities is calculated from your best four or five subjects depending on the stream.
| Marks Range (out of 500) | Percentage | CBSE Grade |
|---|---|---|
| 475 – 500 | 95% – 100% | A1 (10 CGPA) |
| 450 – 474 | 90% – 94.8% | A2 (9 CGPA) |
| 400 – 449 | 80% – 89.8% | B1 (8 CGPA) |
| 350 – 399 | 70% – 79.8% | B2 (7 CGPA) |
| 300 – 349 | 60% – 69.8% | C1 (6 CGPA) |
| 250 – 299 | 50% – 59.8% | C2 (5 CGPA) |
JEE Main — percentile vs percentage
JEE Main ranks candidates by percentile score, not raw percentage. Your percentile shows what percentage of candidates scored below you — not your percentage of correct answers. A 99 percentile means you scored higher than 99% of all test takers. The two terms are often confused but measure very different things.
NEET — marks to percentile
NEET is scored out of 720 marks (180 questions × 4 marks each, with −1 for wrong answers). To find your raw percentage: (Score ÷ 720) × 100. However, NEET counselling and cut-offs are percentile-based across the session. A score of 600+ out of 720 is approximately an 83.3% raw score and typically corresponds to a very high percentile.
Salary Hike Percentage — How It Really Works
Salary hike conversations in India often involve confusion between CTC, in-hand salary, and the actual effective hike. Here is a clear breakdown:
Calculating your hike percentage
Current CTC: ₹9,60,000/year. Offer: ₹11,52,000/year.
% Hike = ((11,52,000 − 9,60,000) ÷ 9,60,000) × 100 = (1,92,000 ÷ 9,60,000) × 100
Why in-hand hike feels smaller
A 20% CTC hike does not mean 20% more in-hand salary. Components like PF employer contribution, gratuity, and performance bonuses are part of CTC but not part of monthly take-home. Your effective in-hand increase is typically 15–18% of the CTC hike depending on your salary structure. Always ask for the revised salary breakup — not just the CTC number — during appraisal.
💡 Negotiation tip: If an employer offers a fixed increment amount (e.g. ₹8,000/month raise), convert it to a percentage yourself before accepting: (8,000 × 12 ÷ Current Annual CTC) × 100. This makes it easier to compare against industry benchmarks and gives you a precise number for the negotiation conversation.
Discount Percentage — Shopping, Sales & EMI
Finding the discount percentage
Discount % = ((MRP − Sale Price) ÷ MRP) × 100
A phone has MRP ₹22,999 and is listed at ₹16,999. What is the effective discount?
Discount % = ((22,999 − 16,999) ÷ 22,999) × 100 = (6,000 ÷ 22,999) × 100
Successive discounts — the trap
When a product gets two successive discounts (e.g. "20% off, then an extra 10% off"), the total discount is not 30%. It is calculated on the reduced price each time:
- Start: ₹1,000
- After 20% off: ₹800
- After extra 10% off on ₹800: ₹720
- Total effective discount: (1,000 − 720) ÷ 1,000 × 100 = 28%, not 30%
🚨 EMI interest trap: When a product advertises "0% interest EMI", check whether the MRP has been inflated to cover the financing cost. Calculate the effective price you are paying across all EMIs and compare it against the cash price or the price on a competing platform. The "discount" and the financing may be offsetting each other.
Common Percentage Calculation Mistakes
1. Confusing percentage point change with percentage change
If interest rates go from 6% to 8%, that is a 2 percentage point increase — but a 33.3% increase in the rate itself ((8−6)÷6×100). These are very different numbers. Financial news often uses "percentage points" and "percent" interchangeably, which causes confusion. Always clarify which is meant.
2. Calculating percentage of a percentage incorrectly
"30% off, and an extra 5% off for UPI payment" does not equal 35% off. You apply 30% first, then 5% of the remaining amount. The combined discount is approximately 33.5%, not 35%.
3. Using the wrong base for percentage increase
Percentage change is always calculated relative to the original (old) value — not the new one. A common mistake is dividing by the new value instead of the old, which gives an incorrect (and usually smaller) percentage.
4. Not accounting for GST when comparing prices
When comparing prices across platforms, ensure both prices include or exclude GST consistently. A ₹10,000 price ex-GST at 18% is actually ₹11,800 — not comparable directly to a competitor's ₹11,000 inclusive price.
5. Assuming percentage decrease reverses a percentage increase
A 25% increase followed by a 25% decrease does not return to the original. ₹1,000 → ₹1,250 (up 25%) → ₹937.50 (down 25%). You end up with less than you started. This matters for investment return calculations and salary cut-and-restore scenarios.
Frequently Asked Questions
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