Percentage calculator
Five quick percentage sums on one page. Type in any box and the answer updates as you go.
Results are rounded for display, to up to 4 decimal places. Terms of use.
How percentages work
Per cent means "out of 100", so 20% is 20/100, or 0.2. Every sum on this page comes from that one idea.
- X% of Y is X / 100 x Y.
- X as a percentage of Y is X / Y x 100.
- Percentage change is (new minus old) / old x 100. A minus result is a fall.
- Increase by X% multiplies by 1 + X / 100; decrease by X% multiplies by 1 minus X / 100.
- Reverse percentage divides by the same factor, to get back to the number before the change.
Example. A jacket is reduced from €150 to €120. The fall is €30, and 30 / 150 x 100 = 20%, so it is 20% off. If you only know the sale price of €120 and the 20% discount, the price before was €120 / 0.8 = €150.
For prices with VAT, the VAT calculator adds or removes VAT at the Irish rates.
Questions
How do I work out a percentage of a number?
Divide the percentage by 100 and multiply by the number. 15% of €240 is 0.15 x 240 = €36.
How do I work out the percentage change between two numbers?
Take the old number from the new one, divide by the old number and multiply by 100. A rent that goes from €1,500 to €1,560 has gone up by 60 / 1,500 x 100 = 4%.
How do I find the price before a discount?
Divide the sale price by 1 minus the discount. A coat that costs €84 after 30% off was €84 / 0.7 = €120. Adding 30% back on to €84 gives €109.20, which is wrong, because the 30% was taken off the higher original price.
Why does a 10% rise and then a 10% fall not bring me back to where I started?
The second percentage is worked out on a different number. €100 up 10% is €110, and €110 down 10% is €99.
What is the difference between percent and percentage points?
If an interest rate goes from 3% to 4%, it has gone up by 1 percentage point, but by 33.3% in relative terms. News reports on rates usually mean percentage points.