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Percentage calculator

A percentage calculator finds what one number is as a proportion of another, scaled to 100. The percentage of a value is calculated as (X ÷ 100) × Y, so 15% of 200 equals 30. Percentage change from an old value to a new value is ((new − old) ÷ |old|) × 100, so 80 rising to 100 is a 25% increase.

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Result

15% of 200

30

result = (X ÷ 100) × Y

Remaining amount
170
As a decimal multiplier
0.15

15% of 200 is 30, found by multiplying 200 by the decimal 0.15. The remaining 85% of 200 is 170.

How to use the percentage calculator

  1. 01

    Choose the calculation

    Select the type of percentage question from the dropdown: a percentage of a number, a percentage change, an increase, a decrease, or a reverse percentage.

  2. 02

    Enter the first value

    Type the percentage into the Value X field, or the starting figure if calculating a change between two numbers.

  3. 03

    Enter the second value

    Type the base number into the Value Y field, or the ending figure if calculating a change.

  4. 04

    Read the result

    The result strip updates as you type and shows the formula applied, along with supporting figures such as the remaining amount and the decimal multiplier.

  5. 05

    Copy the answer

    Press the copy button in the result strip to place the plain-sentence version of the answer on your clipboard.

The formula

result = (X ÷ 100) × Y     change = ((Y − X) ÷ |X|) × 100
X
The percentage, or the starting value when calculating change.
Y
The base value the percentage is taken of, or the ending value when calculating change.
result
The portion of Y represented by X percent.
change
The percentage difference between the starting and ending values, signed.

The word "percent" comes from the Latin per centum, meaning "by the hundred". Dividing by 100 converts a percentage into the decimal multiplier the arithmetic actually uses: 15% is the multiplier 0.15.

Worked example

Calculation
What is 15% of 200?
X
15
Y
200
Result
30

Convert the percentage to a decimal multiplier by dividing by 100: 15 ÷ 100 = 0.15. Multiply that multiplier by the base value: 0.15 × 200 = 30. So 15% of 200 is 30, and the remaining 85% is 170. Reversing the calculation confirms the result: 30 ÷ 200 = 0.15, which is 15%.

Frequently asked questions

How do you calculate a percentage of a number?

Divide the percentage by 100 to get a decimal multiplier, then multiply that multiplier by the number. For 15% of 200, divide 15 by 100 to get 0.15, then multiply 0.15 by 200 to get 30. The same method works for percentages above 100: 250% of 40 is 2.5 × 40, which equals 100.

What is the difference between percentage change and percentage difference?

Percentage change has a designated starting value and is calculated as ((new − old) ÷ |old|) × 100, so it is directional and signed. Percentage difference is symmetric and compares two values against their mean, calculated as (|a − b| ÷ ((a + b) ÷ 2)) × 100. Change answers "how much did it move"; difference answers "how far apart are they".

Why is a 50% decrease not reversed by a 50% increase?

Percentages apply to whatever value is current, not to the original. A 50% decrease takes 100 down to 50. A 50% increase then applies to 50, not to 100, and adds only 25, giving 75. Reversing a 50% decrease requires a 100% increase. This asymmetry is why stacked discounts multiply rather than add.

How do you work out the original price before a discount?

Divide the discounted price by one minus the discount as a decimal. An item selling for $80 after a 20% discount had an original price of 80 ÷ (1 − 0.20), which is 80 ÷ 0.8, or $100. For a price after an increase, divide by one plus the rate instead: $120 after a 20% markup was originally 120 ÷ 1.2, or $100.

What is a percentage point and how does it differ from a percent?

A percentage point is the arithmetic difference between two percentages. An interest rate moving from 4% to 6% has risen by 2 percentage points, but by 50 percent. Financial and statistical reporting uses percentage points precisely to avoid this ambiguity. Confusing the two overstates or understates change by a large margin whenever the base rate is small.

Can a percentage be greater than 100 or negative?

Yes to both. A percentage above 100 simply means the part exceeds the whole, which is normal for growth figures: revenue tripling is a 200% increase. A negative percentage indicates a decrease. Only proportions of a fixed total — such as a share of votes cast — are structurally capped at 100%.

How do you convert a percentage to a fraction or a decimal?

To convert to a decimal, divide by 100: 37.5% becomes 0.375. To convert to a fraction, write the percentage over 100 and reduce: 37.5% becomes 37.5/100, which reduces to 3/8. To go the other way, multiply a decimal by 100 and add a percent sign: 0.045 becomes 4.5%.

Sources

Last reviewed: · Formula and sources verified by Syed Aqeel Ahmad Gillani. See the methodology for how every calculation is derived.

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