Percentages are everywhere — discounts, tips, tax, exam scores, interest and statistics all rely on them. Yet many people freeze when they need to work one out under pressure. The good news is that percentages follow a handful of simple patterns, and once you know them, most calculations become quick mental maths. This guide explains how to calculate the percentages you actually use, with worked examples and a free calculator for when you want a guaranteed answer.
Key takeaways
- "Percent" means "per hundred", so 20% is simply 20 out of 100.
- To find a percentage of a number, multiply by the percentage as a decimal.
- Percentage change compares a new value against the original.
- A calculator removes the risk of mistakes on important numbers.
What a percentage really means
The word "percent" literally means "per hundred". So 25% is 25 out of every 100, or one quarter. Turning a percentage into a decimal is the key skill: just divide by 100. That means 25% becomes 0.25, 8% becomes 0.08, and 150% becomes 1.5. Almost every percentage calculation starts by converting to this decimal form.
Finding a percentage of a number
This is the most common calculation — a discount, a tip, a tax. Multiply the number by the percentage as a decimal. For example, 20% of 80 is 0.20 × 80 = 16. So a 20% discount on an 80 item saves 16, leaving 64 to pay. To add a tip of 15% to a 40 bill, calculate 0.15 × 40 = 6, giving a total of 46. The Percentage Calculator does all of these instantly.
Calculating percentage change
Percentage change tells you how much something has grown or shrunk relative to where it started. The method is: subtract the old value from the new value, divide by the old value, then multiply by 100. If a price rises from 50 to 60, the change is (60 − 50) ÷ 50 × 100 = 20% increase. If it falls from 60 to 45, that is (45 − 60) ÷ 60 × 100 = −25%, a 25% decrease. This is the formula behind price rises, investment returns and statistics.
Reverse percentages
Sometimes you know the result and need the original — for example, a price of 120 that already includes 20% tax, and you want the pre-tax figure. Because 120 represents 120% of the original, you divide by 1.20 to get 100. Reverse percentages trip people up because the instinct is to subtract 20%, which gives the wrong answer. When in doubt, a calculator keeps you right.
Quick mental-maths tricks
- 10% — just move the decimal one place: 10% of 250 is 25.
- 1% — move it two places: 1% of 250 is 2.5.
- 5% — take 10% and halve it.
- Percentages are reversible — 8% of 50 equals 50% of 8, and the second is easier.
Conclusion
Percentages come down to a few reliable patterns: convert to a decimal, multiply to find a percentage of a number, and use the change formula to compare values. Learn the mental-maths shortcuts for everyday speed, and reach for a calculator whenever the number matters. Try the free Percentage Calculator to solve any percentage problem in seconds.
Percentages in everyday finance
Once you are comfortable with percentages, a lot of everyday money maths becomes easy. Interest rates on savings and loans are percentages; so are investment returns, inflation figures, and the tax and tip added to a bill. Discounts in a sale are percentages off, and knowing how to reverse them tells you the original price. Even statistics in the news — "up 12% on last year" — are percentage changes you can now interpret confidently. Being fluent with percentages means you can quickly judge whether a deal is good, how much a rate rise will really cost you, or what a headline figure actually means for your wallet.
A common percentage trap
Watch out for adding and removing the same percentage: a price cut by 20% and then increased by 20% does not return to the original, because the second percentage is calculated on a smaller number. Whenever a calculation involves reversing a percentage, work it out carefully or use a calculator, as intuition often misleads here.
Frequently asked questions
How do I find a percentage of a number?
Multiply the number by the percentage written as a decimal. For example, 20% of 80 is 0.20 × 80 = 16.
How do I calculate percentage change?
Subtract the old value from the new value, divide by the old value, then multiply by 100. A rise from 50 to 60 is a 20% increase.
What is a reverse percentage?
It is finding the original amount before a percentage was added or removed. For a price of 120 that includes 20% tax, divide by 1.20 to get the pre-tax figure of 100.
What is a quick way to find 10%?
Move the decimal point one place to the left. So 10% of 250 is 25, and you can halve that for 5%.