Percentages made simple
"Per cent" literally means "per hundred", so a percentage is just a fraction with 100 on the bottom. Twenty per cent is 20 out of 100, or 0.20 as a decimal. Once you see percentages as decimals, almost every percentage problem becomes a single multiplication.
How to use the percentage calculator
Enter the percentage and the number you want that percentage of, and the calculator returns the result. It is ideal for working out discounts, tips, commissions, test scores, and tax quickly.
The method
To find X% of a number, convert the percentage to a decimal (divide by 100) and multiply. For example, 20% of 350 is 0.20 × 350 = 70. The same logic runs in reverse: if 70 is 20% of a number, divide 70 by 0.20 to recover 350.
Mental-maths shortcuts
Finding 10% is as easy as moving the decimal point one place left, so 10% of 80 is 8. From there you can build almost any percentage: halve the 10% figure for 5%, double it for 20%, or triple it for 30%. To leave a 15% tip on a $60 bill, take 10% ($6), add half of that ($3), and you get $9 without a calculator. These tricks turn percentages from a chore into something you can do in your head at the checkout.