Percentage Calculations Guide: How to Calculate Any Percentage
Basic Percentage Formula
What is X% of Y? Multiply Y by X/100. Example: 15% of £200 = 200 x 0.15 = £30.
What percentage is X of Y? Divide X by Y, multiply by 100. Example: £30 out of £200 = (30/200) x 100 = 15%.
Percentage Change
Increase: ((New - Old) / Old) x 100. If a price goes from £80 to £100: ((100-80)/80) x 100 = 25% increase.
Decrease: Same formula, result is negative. If £100 drops to £80: ((80-100)/100) x 100 = -20% decrease.
Note: a 25% increase followed by a 20% decrease brings you back to the original — they're not the same percentage!
Common Everyday Uses
Discounts: 30% off £60 = £60 x 0.30 = £18 discount, you pay £42.
Tips: 12.5% of £40 = £5. Quick trick: find 10% (£4) and add half of that (£2) = £6.
VAT: To add 20% VAT, multiply by 1.2. To find the pre-VAT price, divide by 1.2.
Pay rises: A 3% raise on £30,000 = £900/year extra, or £75/month before tax.
Quick Mental Maths Tricks
- 10%: Move the decimal point one place left (10% of £45 = £4.50)
- 5%: Half of 10%
- 1%: Move decimal two places left
- 25%: Divide by 4
- 33%: Divide by 3
- Any%: Break it down using 10% and 1% building blocks
Related Calculators
Frequently Asked Questions
How do I calculate a percentage of a number?
Multiply the number by the percentage divided by 100. For example, 15% of £200 = 200 x (15/100) = 200 x 0.15 = £30.
How do I calculate percentage increase or decrease?
Percentage change = ((New Value - Old Value) / Old Value) x 100. A positive result is an increase, negative is a decrease. For example, £80 to £100 = ((100-80)/80) x 100 = 25% increase.