Percentages make a number easier to compare with a whole. The word literally means “per hundred”: 25% means 25 out of every 100. The key to an accurate calculation is choosing the correct whole amount before you do any arithmetic.
Find a percentage of an amount
Convert the percentage to a decimal by dividing by 100, then multiply it by the whole. For example, 15% of 80 is 0.15 × 80 = 12. This method works for discounts, tax estimates, commission and many school problems.
Calculate percentage change
Subtract the old value from the new value. Divide that difference by the old value, then multiply by 100. If a price rises from 50 to 60, the increase is 10. Ten divided by 50 is 0.2, so the percentage increase is 20%.
A common mistake
When a price falls by 20% and then rises by 20%, it does not return to the original price. The second percentage uses a different base. Always state the starting value used in the calculation.
Use results carefully
Percentages explain a relationship; they do not automatically show whether a change is important. Compare the actual amount, the time period and any fees or tax that may apply.
Quick questions
What is 1% of a number?
Divide the number by 100.
Can a percentage be more than 100?
Yes. A result above 100% means the part is larger than the stated whole.
Last reviewed: 5 September 2026. If you spot an error, use our feedback page.