How percentages work
A percentage is a number out of 100. To find 15% of 250, multiply 250 by 0.15 to get 37.5. To find what percent 45 is of 180, divide 45 by 180 and multiply by 100 to get 25%.
Percentage change
Percentage change compares a new value with the original: (new − original) ÷ original × 100. A rise from 80 to 100 is a 25% increase, but a fall from 100 back to 80 is only a 20% decrease, because the starting point is different. This is why a 50% fall followed by a 50% rise leaves you 25% down.
Everyday uses
Percentages come up in sale discounts, pay rises, exam marks, tips and interest rates. For prices including VAT, use the VAT calculator, which handles the maths for adding and removing tax correctly.