How to Calculate a Percentage (3 Simple Ways)
By ToolNimba Editorial Team June 20, 2026 2 min read
A percentage is just a fraction out of 100. The word comes from the Latin for "per hundred", so 25 percent means 25 out of every 100, or 0.25 as a decimal. Almost every real percentage question is one of three types, and once you can spot which type you are looking at, the maths is quick.
Method 1: find a percentage of a number
This is the most common one: a shop takes 20 percent off, or you tip 15 percent. To find a percent of a number, turn the percent into a decimal and multiply.
Formula
Result = (percent divided by 100) times the number. Example: 20 percent of 80 is 0.20 times 80, which is 16.
- Divide the percent by 100 to get a decimal. 20 becomes 0.20.
- Multiply that decimal by the number. 0.20 times 80 equals 16.
- For a discount, subtract from the original: 80 minus 16 leaves 64.
Method 2: what percent is one number of another
Here you have two numbers and want the percentage, for example you scored 18 out of 24 on a test. Divide the part by the whole, then multiply by 100.
Formula
Percent = (part divided by whole) times 100. Example: 18 out of 24 is (18 divided by 24) times 100, which is 75 percent.
Method 3: percentage change (increase or decrease)
Use this when something goes up or down and you want the change as a percent, like a price rising from 50 to 60. Find the difference, divide by the original value, then multiply by 100.
Formula
Change = ((new value minus old value) divided by old value) times 100. From 50 to 60 that is (10 divided by 50) times 100, a 20 percent increase.
A positive answer is an increase and a negative answer is a decrease. The key detail people miss: always divide by the original value, not the new one.
A quick reference table
Common percentages of 200
| Percent | As a decimal | % of 200 |
|---|---|---|
| 5% | 0.05 | 10 |
| 10% | 0.10 | 20 |
| 15% | 0.15 | 30 |
| 25% | 0.25 | 50 |
| 50% | 0.50 | 100 |
Do it instantly
Once you understand the method, a calculator saves time and avoids slips. The tool below handles all three question types and shows the working as you type.
๏ผ Try the free tool Percentage Calculator Free percentage calculator: find what percent of a number, percentage increase or decrease, percent change, percentage difference and reverse percentages fast.For shopping maths specifically, the discount and tip calculators apply method 1 for you and give the final amount directly.
Frequently asked questions
What is the basic percentage formula?
To find a percent of a number, multiply the number by the percent divided by 100. To find what percent one number is of another, divide the part by the whole and multiply by 100.
How do I add a percentage to a number?
Find the percentage of the number, then add it on. To add 20 percent to 80, work out 0.20 times 80 which is 16, then 80 plus 16 gives 96. A shortcut is to multiply by 1.20.
How do I calculate percentage change?
Subtract the old value from the new value, divide that difference by the old value, and multiply by 100. A positive result is an increase and a negative result is a decrease.