Percentage calculator

How to calculate a percentage

A percentage is a fraction with a denominator of 100. Eighteen percent means 18 parts out of 100, or 0.18. To find X% of a number, multiply the number by X and divide by 100. Eighteen percent of 250 is 250 × 18 ÷ 100. First, 250 × 18 = 4,500. Then 4,500 ÷ 100 = 45. So 18% of 250 is 45. In money, 18% of $250.00 is $45.00.

The other two questions are the same relationship rearranged. The part divided by the whole, times 100, is the percent: 45 ÷ 250 × 100 = 18%. If you know the part and the percent, the whole is part × 100 ÷ percent: 45 × 100 ÷ 18 = 250. All three are one proportion. The part is to the whole as the percent is to 100.

Worked example

A shop adds an 8.5% charge to a $64.00 order. The charge is not the whole bill. It is 8.5% of 64.

• Write 8.5% as 8.5 ÷ 100 = 0.085.
• Multiply: 64 × 0.085 = 5.44.
• The charge is $5.44. The total to pay is $69.44.
• Check the reverse: the charge divided by 64, times 100, returns 8.5%.

A few anchors worth memorizing

Ten percent is the number with the decimal point moved one place left: 10% of 64 is 6.4. Five percent is half of that, 3.2. Fifteen percent is the 10% plus the 5%, so 9.6. Twenty-five percent is the same as dividing by 4, and 50% is dividing by 2. One percent is the decimal moved two places. These anchors make a tip or a tax estimate fast, and the calculator is there when the rate is not a friendly fraction.

A percentage can be larger than 100%. If the part is bigger than the reference, the result is over 100: 300 is 150% of 200. That is different from a percent increase, which compares a new value with an old one. For “up 15%” or “down 20%,” use the percentage increase calculator. For a sale sticker, use the discount calculator. Both start from this same definition.

Common percentages of 200