How to Calculate a Percentage: 4 Easy Methods Explained
Percentages appear in shopping discounts, exam results, salary changes, statistics and everyday comparisons. The word percent means “out of 100”, so a percentage turns a part-to-whole comparison into a value that is easy to understand.
Quick answer: to find what percentage one number is of another, divide the part by the whole and multiply by 100.
The basic percentage formula
Percentage = (part ÷ whole) × 100
For example, if you score 42 marks out of 60:
(42 ÷ 60) × 100 = 70%
That means 42 is 70% of 60.
How to find a percentage of a number
To find a percentage of a number, convert the percentage to a decimal and multiply.
15% of 240 = 0.15 × 240 = 36
You can also enter the percentage and number into our Percentage Calculator to check the result quickly.
How to convert a fraction or decimal to a percentage
Multiply a decimal by 100 and add the percent sign. For a fraction, divide the numerator by the denominator first.
- 0.35 becomes 35%.
- 3/8 becomes (3 ÷ 8) × 100 = 37.5%.
How to calculate percentage increase or decrease
Use this formula when a value changes from an original amount to a new amount:
Percentage change = ((new value − original value) ÷ original value) × 100
If a price rises from 80 to 100, the change is:
((100 − 80) ÷ 80) × 100 = 25% increase
For a decrease, the answer will be negative. The Percentage Change Calculator can show the change between two values.
How to calculate marks or exam percentage
For marks, divide marks earned by total marks and multiply by 100. If you earned 72 out of 90:
(72 ÷ 90) × 100 = 80%
Students can use the Marks Percentage Calculator for a quick result. If your course uses different assessment weights, use a weighted-grade method instead of a simple marks percentage.
Percentage difference is not always percentage change
Percentage change normally uses the original value as the baseline. Percentage difference compares two values without treating either one as the starting point, so it uses the average of the two values as the denominator. Choose the method that matches the question.
Common percentage mistakes
- Using the new value instead of the original value as the percentage-change baseline.
- Forgetting to multiply a decimal by 100 when converting it to a percentage.
- Adding percentages when the underlying amounts are different.
- Rounding too early and creating a small final error.
Use a calculator to check your work
For school results, the CGPA to Percentage Calculator can help when you know the conversion scale being used. Always check your school, employer or organisation’s stated conversion rule because different systems may use different formulas.
Once you know whether you need a basic percentage, a percentage change or a weighted result, the correct formula becomes much easier to apply.