Percentage Calculator

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what is 10% of 200, percent of a number

What is X% of Y? Calculate a percentage of a number

The question "what is 10% of 200?" has one answer (20) and a method that works for any number: turn the percent into a decimal and multiply. The calculator below opens in the "what is X% of Y" mode, with 15% of 80 already filled in, and shows the calculation, the result and the value added or subtracted by that percentage.

The method and the mental shortcuts

The method is to divide the percent by 100 and multiply by the value. For 15% of 80: 15 ÷ 100 = 0.15 and 0.15 × 80 = 12. The calculator works with exact fractions, free of floating-point noise, and rounds only on display: 7% of 350 gives exactly 24.5, and 0.5% of 1,200 gives 6. It also shows two supporting values: the value plus the percent (80 + 12 = 92) and the value minus the percent (80 − 12 = 68), which answer "what if I add it" and "what if I take it off" without a second calculation.
The mental shortcuts start from 10%, which is just moving the decimal point one place: 10% of 200 is 20. The others follow: 5% is half of the 10% (10), 20% is double (40), 15% is 10% plus 5% (30), 1% moves two places (2). Some percents are well-known fractions: 50% is dividing by 2, 25% is dividing by 4, 75% is three quarters, and 12.5% is dividing by 8, so 12.5% of 640 is 640 ÷ 8 = 80. For 33.33% divide by 3, knowing the result is an approximation, since 1/3 never ends in decimal.
Three mistakes come up all the time. The first is typing 15 where the calculation needs 0.15: the calculator handles that conversion, but it is worth remembering when using a phone calculator, where the % key varies by device. The second is using the wrong decimal mark: in Brazil the decimal is the comma (12,5), and the period separates thousands. The third is swapping "of" for "on": 20% of 50 is 10, but 50 is 20% on top of what? That is another question, finding the original value, which has its own page. If the question is the reverse, "30 is what percent of 150", the next mode solves it.

Calculations checked by the calculator engine

10% of 200

Input: 10% × 200
Expected output: 20

Move the decimal one place. Added: 220; subtracted: 180.

15% of 80

Input: 15% × 80
Expected output: 12

0.15 × 80. Added: 92; subtracted: 68.

7% of 350

Input: 7% × 350
Expected output: 24,5

0.07 × 350 = exactly 24.5. Added: 374.5.

12.5% of 640

Input: 12,5% × 640
Expected output: 80

Equivalent to dividing by 8.

0.5% of 1,200

Input: 0,5% × 1.200
Expected output: 6

Half a percent is 0.005 of the value.

Full tool FAQ

How do I work out a percentage in my head?

Start with 10%, which is the value divided by 10, and build the rest from it: 1% is dividing by 100, 5% is half of 10%, 20% is double 10%, 25% is dividing by 4 and 50% is dividing by 2. For 15% of 80, take 10% (8) plus 5% (4), which is 12. For 35% of 200, add 30% (60) and 5% (10), which is 70. If the numbers are awkward, swap the order: 8% of 50 equals 50% of 8, which is 4.

How do I calculate X% of a value?

How do I find what percent one number is of another?

How do I calculate a percentage increase or discount and the final value?

How do I calculate the percent change between two values?

How do I find the original value before a discount or increase?

Why don't two successive discounts add up? What is 20% and then 10%?

What is the difference between a percentage point and a percent?

What is the difference between margin and markup, and how do I convert?

How do I calculate a tip and split the bill between people?

How do I calculate a change repeated over several periods?

Does the calculator round? Why doesn't 0.30000000000000004 show up?

Frequently asked questions

How do I work out 10% of a value in my head?

Move the decimal point one place to the left: 10% of 350 is 35, and 10% of 49.90 is 4.99. From there you get 5% (half), 20% (double) and 15% (10% plus 5%).

What is the formula for a percent of a number?

Divide the percent by 100 and multiply by the value: 15% of 80 is 0.15 × 80 = 12. In a spreadsheet, the same calculation is =80*15%.

Why does my phone calculator give a different result with the % key?

Because the % key behaves differently across devices: on some, 200 + 10% adds 10% of 200; on others, it only divides by 100. Here the calculation is always explicit, and the added value shows alongside.

Next steps

What is X% of Y? Calculate a percentage of a number

The method and the mental shortcuts

The method is to divide the percent by 100 and multiply by the value. For 15% of 80: 15 ÷ 100 = 0.15 and 0.15 × 80 = 12. The calculator works with exact fractions, free of floating-point noise, and rounds only on display: 7% of 350 gives exactly 24.5, and 0.5% of 1,200 gives 6. It also shows two supporting values: the value plus the percent (80 + 12 = 92) and the value minus the percent (80 − 12 = 68), which answer "what if I add it" and "what if I take it off" without a second calculation.

The mental shortcuts start from 10%, which is just moving the decimal point one place: 10% of 200 is 20. The others follow: 5% is half of the 10% (10), 20% is double (40), 15% is 10% plus 5% (30), 1% moves two places (2). Some percents are well-known fractions: 50% is dividing by 2, 25% is dividing by 4, 75% is three quarters, and 12.5% is dividing by 8, so 12.5% of 640 is 640 ÷ 8 = 80. For 33.33% divide by 3, knowing the result is an approximation, since 1/3 never ends in decimal.

Three mistakes come up all the time. The first is typing 15 where the calculation needs 0.15: the calculator handles that conversion, but it is worth remembering when using a phone calculator, where the % key varies by device. The second is using the wrong decimal mark: in Brazil the decimal is the comma (12,5), and the period separates thousands. The third is swapping "of" for "on": 20% of 50 is 10, but 50 is 20% on top of what? That is another question, finding the original value, which has its own page. If the question is the reverse, "30 is what percent of 150", the next mode solves it.

Calculations checked by the calculator engine

10% of 200

Input: 10% × 200
Expected output: 20

Move the decimal one place. Added: 220; subtracted: 180.

15% of 80

Input: 15% × 80
Expected output: 12

0.15 × 80. Added: 92; subtracted: 68.

7% of 350

Input: 7% × 350
Expected output: 24,5

0.07 × 350 = exactly 24.5. Added: 374.5.

12.5% of 640

Input: 12,5% × 640
Expected output: 80

Equivalent to dividing by 8.

0.5% of 1,200

Input: 0,5% × 1.200
Expected output: 6

Half a percent is 0.005 of the value.

Full tool FAQ

How do I work out a percentage in my head?

How do I calculate X% of a value?

How do I find what percent one number is of another?

How do I calculate a percentage increase or discount and the final value?

How do I calculate the percent change between two values?

How do I find the original value before a discount or increase?

Why don't two successive discounts add up? What is 20% and then 10%?

What is the difference between a percentage point and a percent?

What is the difference between margin and markup, and how do I convert?

How do I calculate a tip and split the bill between people?

How do I calculate a change repeated over several periods?

Does the calculator round? Why doesn't 0.30000000000000004 show up?

Frequently asked questions

How do I work out 10% of a value in my head?

Move the decimal point one place to the left: 10% of 350 is 35, and 10% of 49.90 is 4.99. From there you get 5% (half), 20% (double) and 15% (10% plus 5%).

What is the formula for a percent of a number?

Divide the percent by 100 and multiply by the value: 15% of 80 is 0.15 × 80 = 12. In a spreadsheet, the same calculation is =80*15%.