What is the formula to calculate percentage?

Percentage = (Part ÷ Whole) × 100. Example: what percent of 80 is 20? Answer: (20 ÷ 80) × 100 = 25%. To find a percentage of a number: multiply the number by the percentage and divide by 100. Example: 30% of 150 = (30 × 150) ÷ 100 = 45.

How do I calculate percentage increase or decrease?

Percentage change = ((New Value − Old Value) ÷ Old Value) × 100. If positive, it's an increase; if negative, a decrease. Example: price rose from $50 to $65 → ((65−50)÷50)×100 = 30% increase. Example: price fell from $80 to $60 → ((60−80)÷80)×100 = −25% decrease.

What is the difference between percentage and percentage points?

A percentage point is an absolute difference between two percentages. If interest rates rise from 3% to 5%, that is a 2 percentage point increase — but a 66.7% relative increase ((5−3)÷3×100). Politicians and media often confuse these: saying a policy 'cut unemployment by 2%' when they mean 2 percentage points (from 8% to 6%) dramatically understates the actual relative reduction.

How do I reverse a percentage (find the original value)?

To find the original value before a percentage was applied: Original = Final Value ÷ (1 + percentage/100) for increases. Example: a price after 20% tax is $120 → original = 120 ÷ 1.20 = $100. For decreases: Original = Final Value ÷ (1 − percentage/100). Example: price after 25% discount is $75 → original = 75 ÷ 0.75 = $100.

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Percentage Formulas

What percent of B is A?

% = (A ÷ B) × 100

What is A% of B?

Result = (A / 100) × B

Increase B by A%

Result = B × (1 + A/100)

Frequently Asked Questions

What is 20% of 150?

20% of 150 = (20 ÷ 100) × 150 = 30. Quick mental math: 10% of 150 is 15, so 20% is 30.

How do I add a percentage to a number?

Multiply the number by (1 + percentage/100). To add 15% to $200: $200 × 1.15 = $230. To add 7.5% sales tax to $50: $50 × 1.075 = $53.75.

What percentage is 45 out of 60?

(45 ÷ 60) × 100 = 75%. General formula: (part ÷ whole) × 100.

How do I work out a discount percentage?

Discount % = ((Original Price − Sale Price) ÷ Original Price) × 100. A $80 item on sale for $60: ((80−60)÷80)×100 = 25% off.

Decrease B by A%

Result = B × (1 − A/100)

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The Three Types of Percentage Questions

Every percentage problem is one of three types. Type 1: What is X% of Y? Multiply: X/100 × Y. What is 15% of 80? 0.15 × 80 = 12. Type 2: X is what percent of Y? Divide and multiply: (X/Y) × 100. 12 is what percent of 80? (12/80) × 100 = 15%. Type 3: X is Y% of what? Divide: X/(Y/100). 12 is 15% of what? 12/0.15 = 80. Recognizing the type first makes any percentage problem solvable with a single formula.

Percentages appear everywhere in daily life: sales tax (add Y% to price), discounts (subtract Y% from price), tips (add 18–20% to bill), grade calculation (score/total × 100), inflation (price increase %), nutritional labels (% daily value), interest rates (annual %), and statistics (approval ratings, poll margins). A mental shortcut: 10% of any number is just moving the decimal one place left. 15% = 10% + 5% (half of 10%).

Common Percentage Shortcuts

To Find	Method	Example
10% of X	X ÷ 10	10% of 250 = 25
5% of X	X ÷ 20	5% of 250 = 12.5
25% of X	X ÷ 4	25% of 250 = 62.5
20% of X	X ÷ 5	20% of 250 = 50
1% of X	X ÷ 100	1% of 250 = 2.5