How to calculate percentages without overthinking it

A percentage is a way to describe a part out of 100. To calculate a percentage of a number, turn the percentage into a decimal and multiply it by the base number.

For example, to calculate 20% of 350:

350 x 20 / 100 = 70

You can also write it as:

350 x 0.20 = 70

The basic percentage formula

The core formula is:

part / total x 100

Use it when you want to know what percentage one value represents out of another. If you want the opposite operation, such as finding 20% of 350, use:

percentage / 100 x number

Finding what percentage one number is of another

If you want to know what percentage 45 is of 200, divide the part by the total and multiply by 100:

45 / 200 x 100 = 22.5%

That means 45 represents 22.5% of 200.

For a more focused walkthrough, read what percentage is one number of another.

Increases and decreases

To calculate percentage change between two values, subtract the original value from the new value, divide by the original value and multiply by 100.

(new value - original value) / original value x 100

If a value goes from 80 to 100:

(100 - 80) / 80 x 100 = 25%

The result is a 25% increase. If the result is negative, it is a percentage decrease.

You can see that case in more detail in the guide to percentage increase.

Common mistakes

The most common mistake is using the wrong base. A 15% change on 1,000 is not the same as a 15% change on 850, even though the percentage is identical.

Another mistake is mixing percentages with percentage points. Going from 20% to 30% is a difference of 10 percentage points, but the relative increase is 50% because 10 is half of 20.

When to use a calculator

Mental math is often enough for quick estimates. When you compare prices, taxes, grades, budgets or changes over time, a calculator helps avoid small mistakes that can change the final decision.

Use the percentage calculator when you want the answer and the formula side by side.