How to Calculate a Percentage (With Examples)

Quick answer: To find what percentage one number is of another, divide the part by the total and multiply by 100. For example, 25 out of 200 is 25 ÷ 200 × 100 = 12.5%. The same idea, rearranged, also gives you a percent of a number and the percent change between two values.

The basic percentage formula

A percentage is a fraction written out of 100. The word comes from the Latin per centum, meaning “by the hundred.” The core formula is:

percentage = (part ÷ total) × 100

The part is the amount you are measuring, and the total is the whole it belongs to. If 18 of 24 tasks are finished, the part is 18 and the total is 24: 18 ÷ 24 = 0.75, and 0.75 × 100 = 75%.

Two other questions use the same relationship:

• Percent of a number: part = total × (percentage ÷ 100). For 15% of 80: 80 × 0.15 = 12.
• Percent change: change = (new − old) ÷ old × 100. From 50 to 65: (65 − 50) ÷ 50 × 100 = 30% increase.

How to use the free Percentage Calculator

The calculator answers one question: what percentage is one value of another?

1. Enter the part in the Value field, for example 25.
2. Enter the whole in the Total field, for example 200.
3. Click Calculate percentage.
4. Read the sentence that appears, for example 25 is 12.5% of 200.
5. Click Copy result if you want to paste the sentence somewhere else.

Results are shown with up to six decimal places. If the total is zero, the tool shows The total must be greater than zero. because dividing by zero has no answer. The calculator does not work out percent change or a percent of a number directly; use the formulas above for those, or rearrange your question so it asks what percentage one value is of another.

Worked examples

To check the first two in the calculator, enter 25 and 200, then 34 and 40. For the price change, enter the difference (15) as the Value and the old price (50) as the Total; the tool returns 30%.

Percent change versus percentage points

When you compare two percentages, there are two different ways to describe the gap. If a conversion rate moves from 4% to 5%, it has risen by 1 percentage point. As a relative change, it has risen by 25%, because (5 − 4) ÷ 4 × 100 = 25.

Both statements are correct, but they mean different things. Say which one you are using, especially in reports, so readers do not mistake a small absolute change for a large one or the other way around.

Common mistakes

• Dividing by the wrong number. Percent change is always measured against the starting value. A rise from 50 to 65 is 30%, not 23% (which is 15 ÷ 65).
• Adding percentage changes together. A 10% increase followed by a 10% decrease does not return to the start: 100 becomes 110, then 99.
• Mixing units. Make sure the part and total use the same unit, such as both in minutes or both in hours.
• Forgetting to multiply by 100. 18 ÷ 24 = 0.75, which is 75%, not 0.75%.
• Using a total of zero. A percentage of nothing is undefined. If the starting value is zero, describe the change in absolute numbers instead.
• Rounding too early. Keep full precision during the calculation and round only the final answer.

Quick mental shortcuts

• 10%: move the decimal point one place left. 10% of 340 is 34.
• 5%: half of 10%. 5% of 340 is 17.
• 1%: move the decimal point two places left. 1% of 340 is 3.4.
• Swap the numbers: x% of y equals y% of x. 8% of 50 is the same as 50% of 8, which is 4.

These shortcuts are useful for checking that a calculator result is in the right range before you rely on it.