Calculators
Percent calculator with the formula shown
To find a percentage of a number, multiply the two numbers and divide by 100, so 15% of 200 is 30. This online percent calculator does that and four other calculations: what percent one number is of another, percentage change, adding a percentage and subtracting a percentage. It runs in your browser and shows each formula with your numbers.
Uses native floating-point arithmetic (about 15–17 significant digits). Inputs and results may be rounded; this is not exact arbitrary-precision arithmetic.
How to use the percentage calculator
The page has one form with five calculation types. The two field labels change to match the type you pick.
- Under Calculation type, choose Percentage of a number, What percent?, Percentage change, Add percentage or Subtract percentage.
- Check the field labels. Percentage of a number, Add percentage and Subtract percentage ask for Percentage and Number. What percent? asks for Part and Whole (nonzero). Percentage change asks for Original value (nonzero) and New value.
- Type numbers with a dot for decimals. Leave out commas, spaces, % signs and currency signs, so a money amount of $80 goes in as 80. Negative numbers and scientific notation such as 1e6 work.
- Select Calculate. The Result panel shows the answer, a line that names the calculation, and the Formula with your numbers in it.
- Select Copy result to copy the answer, or Download text to save a report named percentage-calculation.txt.
Reset brings back the starting example, 15% of 200. Changing a field or the calculation type clears the old result.
Percentage formulas with worked examples
A percentage is a number out of 100, so each formula here multiplies or divides by 100. P is the percentage and N is the number. Each example shows the calculator's result.
- Percentage of a number uses P × N / 100. For 12.5% of 80, 12.5 × 80 / 100 = 10.
- What percent? uses Part / Whole × 100 to give a part as a percentage of a total. For 42 out of 50, 42 / 50 × 100 = 84%.
- Percentage change uses (New − Original) / Original × 100. From 200 to 150, (150 − 200) / 200 × 100 = -25%, a percentage decrease.
- Add percentage uses N × (1 + P / 100). 50 plus 20% is 50 × 1.2 = 60.
- Subtract percentage uses N × (1 − P / 100). 80 minus 25% is 80 × 0.75 = 60.
Percentage change divides by the signed original value. A change from -100 to -50 gives -50%, even though the number went up. Percentage points are a different measure. A rate that moves from 20% to 30% rises by 10 points, and its percentage change is 50%.
What the result and the text report show
The Result panel shows the full value the browser computes, with no rounding step. What percent? and Percentage change answers end in a percent sign. The other three types give a number with no percent sign, so 15% of 200 shows 30.
Below the answer, a line names the calculation, such as 15% of 200 or Percentage increase from the original value. The Formula line repeats the formula with your numbers in parentheses and the result at the end, as in (15) × (200) / 100 = 30.
Copy result copies only the answer. If the browser blocks clipboard access, the page selects the answer so you can copy it by hand.
Download text saves percentage-calculation.txt. The report lists the calculation type, both inputs as the calculator read them, the result, the formula and the explanation line. It ends with a note on floating-point precision.
Limits
The calculator does five calculation types and nothing else. It cannot work backwards to find the whole from a part and a percent, as in 20 is 40% of what number. It cannot find the price before a discount, a raise or sales tax. It has no percent difference, percent error or percentage-point mode.
Add percentage and Subtract percentage return the final value only. To see the amount added or taken off, run Percentage of a number with the same inputs.
Commas, spaces inside a number, % signs, currency signs and fractions such as 1/8 give an error. What percent? needs a nonzero whole, and Percentage change needs a nonzero original value.
The math uses the browser's floating-point numbers, with about 15 to 17 significant digits and no rounding control. Adding 15% to 200 shows 229.99999999999997, because 1.15 has no exact binary form. Tiny or huge results use scientific notation, so 0.0001% of 0.5 shows 5.000000000000001e-7. Inputs or results outside the browser's numeric range give an error.
Questions
How do I calculate a percentage of an amount?
Multiply the amount by the percentage, then divide by 100. For 15% of 200, that is 15 × 200 / 100 = 30. On this page, choose Percentage of a number, enter 15 in Percentage and 200 in Number, then select Calculate. The Formula line shows the same steps with your numbers.
How much is 20% out of 70?
20% of 70 is 14, because 20 × 70 / 100 = 14. If you mean the percentage of two numbers, 20 out of 70, the answer is 20 / 70 × 100, which the calculator shows as 28.57142857142857%. Use Percentage of a number for the first reading and What percent? for the second.
What is 30% of 20?
30% of 20 is 6. Multiply 30 by 20 to get 600, then divide by 100. The order does not change the answer, so 20% of 30 is also 6. Enter 30 as the Percentage and 20 as the Number, and the Formula line reads (30) × (20) / 100 = 6.
Can you take a percent of a percent?
Yes. To find a percentage of a percentage, multiply the two and divide by 100, so 20% of 50% is 20 × 50 / 100 = 10%. On this page, choose Percentage of a number, then enter 20 in Percentage and 50 in Number without the % signs. The result shows 10 with no percent sign, which here means 10%.
How do I find out what percent of a number is another number?
Divide the part by the whole and multiply by 100. For a test score of 42 out of 50, 42 / 50 × 100 = 84%. Choose What percent?, type 42 in Part and 50 in Whole (nonzero), and select Calculate. The whole cannot be zero, because the formula divides by it.
How do I add a percentage to a number?
Multiply the number by 1 plus the percentage divided by 100, so adding 10% to 30 gives 30 × (1 + 10 / 100) = 33. On this page, choose Add percentage, enter 10 in Percentage and 30 in Number, then select Calculate. The result is the new total. To see the 3 added, run Percentage of a number with 10 and 30.
How do I find the percent off of a number?
Choose Subtract percentage, then enter the discount in Percentage and the price, without the $ sign, in Number. For 25% off 80, the result is 60, since 80 × (1 − 25 / 100) = 60. The page shows the sale price only. To see the 20 you save, run Percentage of a number with 25 and 80.