How to Calculate Percentages: 5 Essential Methods
Percentages are everywhere—shopping discounts, exam scores, salary raises, interest rates, statistics. Whether you're calculating a tip, figuring out sale prices, or analyzing data, knowing how to work with percentages is essential.
This guide covers the 5 most common percentage calculations you'll need in everyday life, complete with formulas and real-world examples.
Method 1: What is A% of B?
Formula: (A ÷ 100) × B
This is the most basic percentage calculation. You're finding what portion of a number a certain percentage represents.
A shirt costs ₹1,500 and there's a 25% discount. How much is the discount?
Solution: (25 ÷ 100) × 1,500 = 0.25 × 1,500 = ₹375
The discount is ₹375, so you pay ₹1,125.
You scored 85% on a 200-mark exam. How many marks did you get?
Solution: (85 ÷ 100) × 200 = 0.85 × 200 = 170 marks
Method 2: What Percent is A of B?
Formula: (A ÷ B) × 100
You have two numbers and want to know what percentage the first number is of the second.
You answered 45 out of 60 questions correctly. What's your percentage?
Solution: (45 ÷ 60) × 100 = 0.75 × 100 = 75%
You've saved ₹12,000 toward your ₹50,000 goal. What percentage have you saved?
Solution: (12,000 ÷ 50,000) × 100 = 0.24 × 100 = 24%
Method 3: Percentage Increase
Formula: ((New Value - Old Value) ÷ Old Value) × 100
Calculate how much something increased as a percentage of the original value.
Your salary increased from ₹40,000 to ₹50,000. What's the percentage increase?
Solution: ((50,000 - 40,000) ÷ 40,000) × 100
= (10,000 ÷ 40,000) × 100 = 0.25 × 100 = 25% increase
Petrol price rose from ₹95 to ₹104 per liter. Calculate percentage increase.
Solution: ((104 - 95) ÷ 95) × 100
= (9 ÷ 95) × 100 = 9.47% increase
Method 4: Percentage Decrease
Formula: ((Old Value - New Value) ÷ Old Value) × 100
Calculate how much something decreased as a percentage of the original value.
You weighed 80 kg and now weigh 72 kg. What's the percentage decrease?
Solution: ((80 - 72) ÷ 80) × 100
= (8 ÷ 80) × 100 = 0.1 × 100 = 10% decrease
A laptop was ₹60,000, now on sale for ₹45,000. Percentage discount?
Solution: ((60,000 - 45,000) ÷ 60,000) × 100
= (15,000 ÷ 60,000) × 100 = 25% discount
Method 5: Find the Original Value
Formula: (Final Value × 100) ÷ Percentage
You know the final value after a percentage was applied, and need to find the original.
You paid ₹11,800 including 18% GST. What was the original price?
Solution: Original + 18% of Original = ₹11,800
Original × 1.18 = ₹11,800
Original = 11,800 ÷ 1.18 = ₹10,000
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Free Percentage Calculator →Common Percentage Mistakes to Avoid
Mistake 1: Using the Wrong Base
When calculating percentage change, always use the original value as the base, not the new value.
Wrong: Price went from ₹100 to ₹150. Using 150 as base: (50÷150)×100 = 33.3%
Right: Using 100 as base: (50÷100)×100 = 50%
Mistake 2: Confusing "Of" and "More Than"
"50% of 100" = 50 (you're finding half)
"50% more than 100" = 150 (you're adding half to the original)
Mistake 3: Adding Percentages Directly
A 20% increase followed by a 20% decrease does NOT bring you back to the original!
Example: Start with 100 → +20% = 120 → -20% of 120 = 96 (not 100!)
Real-World Applications
1. Shopping & Discounts
Calculate final prices after discount, compare deals, determine savings.
2. Finance & Investing
Calculate returns, interest rates, profit margins, tax amounts.
3. Health & Fitness
Track weight loss/gain, body fat percentage, macronutrient ratios.
4. Business & Analytics
Growth rates, conversion rates, market share, year-over-year comparisons.
5. Education
Exam scores, attendance tracking, grade calculations.
Quick Reference Cheat Sheet
| What You Want | Formula |
|---|---|
| A% of B | (A÷100)×B |
| A is what % of B | (A÷B)×100 |
| % increase | ((New-Old)÷Old)×100 |
| % decrease | ((Old-New)÷Old)×100 |
| Increase B by A% | B×(1+A/100) |
| Decrease B by A% | B×(1-A/100) |
Practice Makes Perfect
The best way to master percentages is practice. Try these exercises:
- A restaurant bill is ₹1,200. Calculate 15% tip.
- Your phone's battery was at 80% and dropped to 35%. What % did it lose?
- A stock price rose from ₹250 to ₹310. Calculate % gain.
- After a 30% discount, a watch costs ₹4,200. What was the original price?
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