Result
30
Finance · Everyday math
Percentage
Percentage
calculator
Every kind of percentage question, answered the moment you type. Percent of a number, what percent one number is of another, change between two numbers, and adding or subtracting a percent.
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%
As a fraction
30 / 200
Percentage
15%
As a decimal
0.15
Change
+15%
Difference
+30
%
New value
230
Amount of change
+30
How to calculate a percentage
A percentage is just a fraction of 100. "Per cent" literally means "per hundred", so 15% is another way of writing 15 out of 100, or the decimal 0.15. Every percentage question below is a small rearrangement of the same relationship between a part, a whole, and a rate.
The core formula
part = rate ÷ 100 × whole
Percent of a number
The most common question: what is a given percent of a value? Divide the rate by 100 and multiply by the whole.
Worked example — 15% of 200
15 ÷ 100 = 0.15
0.15 × 200 = 30
0.15 × 200 = 30
What percent one number is of another
Turn it around when you have the part and the whole but want the rate. Divide the part by the whole, then multiply by 100.
Worked example — 30 out of 200
30 ÷ 200 = 0.15
0.15 × 100 = 15%
0.15 × 100 = 15%
Percentage increase and decrease
To measure change between two numbers, take the difference, divide by the starting value, then multiply by 100. A positive answer is an increase; a negative answer is a decrease. Dividing by the start — not the end — is the step people most often get wrong.
Worked example — 200 rising to 230
230 − 200 = 30
30 ÷ 200 × 100 = +15%
30 ÷ 200 × 100 = +15%
Adding or subtracting a percent
To grow a number by a percent, multiply by one plus the rate. To shrink it, multiply by one minus the rate. This is how tips, discounts and tax are applied.
Worked example — 200 plus 15%
200 × (1 + 0.15) = 200 × 1.15 = 230
Where you'll use this
Percentages run through everyday money and measurement: a tip on a restaurant bill, a discount in a sale, sales tax or VAT added at the till, interest on savings, a test score, or the change in a price week to week. The same four moves above cover almost all of them.
A quick note on percentage points
Percentage change and percentage points are not the same thing. If a rate moves from 10% to 15%, that is a rise of 5 percentage points, but a 50% increase in relative terms. Reporting one as the other is a classic way to make a small change sound big — worth keeping straight.
Common questions
Percentage FAQ
Divide the percentage by 100 and multiply by the number. For 15% of 200: 15 ÷ 100 = 0.15, then 0.15 × 200 = 30. The % of tab above does this live.
Divide the part by the whole and multiply by 100. 30 out of 200 is 30 ÷ 200 × 100 = 15%. Use the is what % tab.
Subtract the old value from the new value, divide by the old value, then multiply by 100. From 200 to 230: (230 − 200) ÷ 200 × 100 = +15%. A negative result is a decrease. The change tab handles both.
Multiply the number by (1 + percent ÷ 100). To add 15% to 200: 200 × 1.15 = 230. To subtract a percent, use (1 − percent ÷ 100). The ± percent tab does both.
Percentage change is measured relative to the starting value; percentage points are the plain arithmetic gap between two percentages. Going from 10% to 15% is a 5 percentage-point rise, but a 50% increase.
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