How to Calculate Percentage of a Number (3 Methods With Examples)

"What's 18% of 4,500?" is the kind of question that comes up almost daily — shopping discounts, tax calculations, tip amounts, salary hikes, exam scores. Yet many people fumble the math or second-guess themselves. Here are three ways to do it, from simplest to most versatile.

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Method 1: The Basic Formula

Percentage of a number = Number × Percentage / 100

Question	Calculation	Answer
What is 10% of 500?	500 × 10 / 100	50
What is 15% of 1,200?	1,200 × 15 / 100	180
What is 18% of 4,500?	4,500 × 18 / 100	810
What is 7.5% of 10,000?	10,000 × 7.5 / 100	750
What is 33% of 900?	900 × 33 / 100	297
What is 2.5% of 80,000?	80,000 × 2.5 / 100	2,000

Method 2: Convert to Decimal

Percentage as decimal = Percentage / 100

Then just multiply: Number × Decimal

Percentage	As Decimal	10% of 350	25% of 800
5%	0.05	—	—
10%	0.10	350 × 0.10 = 35	—
15%	0.15	—	—
20%	0.20	—	—
25%	0.25	—	800 × 0.25 = 200
50%	0.50	—	—
75%	0.75	—	—

Method 3: Mental Math Shortcuts

To Find	Shortcut	Example
10%	Move decimal one place left	10% of 850 = 85
5%	Find 10%, halve it	5% of 850 = 85/2 = 42.50
1%	Move decimal two places left	1% of 850 = 8.50
15%	10% + 5%	15% of 200 = 20 + 10 = 30
20%	10% × 2	20% of 450 = 45 × 2 = 90
25%	Divide by 4	25% of 800 = 200
33%	Divide by 3	33% of 900 = 300
50%	Divide by 2	50% of 750 = 375
75%	50% + 25%	75% of 800 = 400 + 200 = 600

The Three Types of Percentage Problems

Type 1: Find the percentage of a number

"What is 12% of ₹5,000?" Answer = 5,000 × 12/100 = ₹600

Type 2: Find what percentage one number is of another

"₹600 is what percent of ₹5,000?" Percentage = (600 / 5,000) × 100 = 12%

Type 3: Find the original number

"12% of what number is ₹600?" Original = 600 / (12/100) = 600 / 0.12 = ₹5,000

Percentage Increase and Decrease

Percentage Increase

Formula: Increase % = (New − Old) / Old × 100

Old Value	New Value	Increase %
₹50,000	₹58,000	(58,000−50,000)/50,000 × 100 = 16%
₹100	₹135	35%
₹1,200	₹1,500	25%

Percentage Decrease

Formula: Decrease % = (Old − New) / Old × 100

Old Value	New Value	Decrease %
₹5,000	₹4,250	(5,000−4,250)/5,000 × 100 = 15%
₹80	₹60	25%

Reverse: Finding Final Price After Discount

Final price = Original × (1 − Discount%/100)

Original	Discount	You Pay
₹2,000	10% off	₹2,000 × 0.90 = ₹1,800
₹5,000	30% off	₹5,000 × 0.70 = ₹3,500
₹15,000	40% off	₹15,000 × 0.60 = ₹9,000

Common Percentage Mistakes

Mistake 1: Adding percentages of different bases. A 20% increase followed by a 20% decrease does NOT return to the original. ₹100 → +20% → ₹120 → −20% → ₹96. You lost ₹4 (4%). Mistake 2: Percentage points vs percentage change. Interest rate going from 8% to 10% is a 2 percentage point increase but a 25% increase (2/8 × 100). Mistake 3: Reversing a percentage. If an item is ₹1,180 after 18% GST, the base price is NOT ₹1,180 × 0.82 = ₹967.60. It's ₹1,180 / 1.18 = ₹1,000. The GST was calculated on ₹1,000, not ₹1,180.

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How do I calculate percentage on a basic calculator?

Enter the number, press ×, enter the percentage, press %. Example: 4500 × 18 % = 810. If your calculator doesn't have a % key: 4500 × 18 ÷ 100 = 810.

What's the percentage formula for exam marks?

Percentage = (Marks obtained / Total marks) × 100

Scored 432 out of 500? Percentage = (432/500) × 100 = 86.4%.

How do I calculate salary hike percentage?

Hike % = (New salary − Old salary) / Old salary × 100

Old: ₹50,000. New: ₹58,000. Hike = (8,000/50,000) × 100 = 16% hike.

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