Calculators
How to Calculate Percentage: 3 Methods With Examples
Percentage calculations come up constantly — exam scores, discounts, salary raises, tax amounts, budget splits. There are three core questions, each with its own formula. Here's how each one works, with real examples.
Method 1: What is X% of a number?
This is the most common percentage calculation. The formula is: Result = (Percentage ÷ 100) × Number
A quick mental shortcut: to find 10%, move the decimal one place left. 10% of 340 is 34. For 5%, halve that (17). For 20%, double the 10% figure (68). These shortcuts get you close without a calculator for common percentages.
Method 2: X is what percentage of Y?
Use this when you have two values and want to express the relationship as a percentage. Formula: Percentage = (Part ÷ Whole) × 100
Method 3: Percentage change between two values
Use this when a value has changed and you want to quantify the change as a percentage. Formula: % Change = ((New − Old) ÷ |Old|) × 100
A positive result is an increase. Negative is a decrease. The starting value is in the denominator — if it is negative, use its absolute value (|old|) to get a result that reads correctly.
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Use the calculator →Frequently asked questions
How do you calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 20% of 150: (20 ÷ 100) × 150 = 0.20 × 150 = 30. This works for any percentage — 15% of 200 is 0.15 × 200 = 30. If you are calculating a tip, tax, or discount, this is the formula to use.
How do you find what percentage one number is of another?
Divide the part by the whole and multiply by 100. If you scored 43 out of 60, that is (43 ÷ 60) × 100 = 71.67%. If £240 of a £1,200 budget has been spent, that is (240 ÷ 1200) × 100 = 20%. The result is always a percentage that shows how the smaller value relates to the larger one.
How do you calculate percentage increase?
Subtract the original value from the new value, divide by the original value, then multiply by 100. Formula: ((new − old) ÷ old) × 100. If a salary goes from £32,000 to £35,200, the increase is ((35200 − 32000) ÷ 32000) × 100 = (3200 ÷ 32000) × 100 = 10%. A positive result means an increase.
How do you calculate percentage decrease?
The formula is identical to percentage increase: ((new − old) ÷ old) × 100. A negative result means a decrease. If a price drops from £80 to £60, that is ((60 − 80) ÷ 80) × 100 = (−20 ÷ 80) × 100 = −25%. The absolute value (25%) is the size of the decrease.
What is the difference between percentage and percentage points?
Percentage is a ratio expressed out of 100. Percentage points are the arithmetic difference between two percentages. If interest rates go from 3% to 5%, that is a 2 percentage point increase but a 66.7% increase (because (5−3)÷3 × 100 = 66.7%). This distinction matters in finance, statistics, and news reporting where the two are often confused.
How do you work backwards from a percentage?
If you know the result of applying a percentage and want the original number, divide by the percentage expressed as a decimal. If a price after a 20% discount is £64, the original was £64 ÷ 0.80 = £80. The principle is: original × (1 − rate) = discounted price, so original = discounted price ÷ (1 − rate).