Key takeaways
- Percentage = (part ÷ whole) × 100.
- The part always goes on top of the fraction, the whole on the bottom.
- A percentage can be over 100% when the part is bigger than the whole.
- Don't forget to multiply by 100 — a decimal alone isn't a percentage.
In this guide
What is a percentage?
"Percent" means "out of 100". A percentage turns a part-to-whole comparison into a number out of 100, so it's easy to compare test scores, discounts, or progress.
Why does percentage matter?
Percentages let you compare things that started out with different totals. A score of 18/25 and a score of 34/50 are hard to compare directly, but as percentages (72% and 68%) it's immediately clear which is higher.
100% always means the whole thing. Anything above 100% means the part is actually bigger than the original whole, like a value that has grown beyond where it started.
The formula
| Symbol | What it means | Example |
|---|---|---|
| Percentage | The result, shown with a % sign | 72% |
| part | The smaller amount you're measuring | 18 |
| whole | The total the part is compared to | 25 |
How to calculate a percentage step by step
- 1Identify the part and the whole in your problem.
- 2Divide the part by the whole to get a decimal:
18 ÷ 25 = 0.72. - 3Multiply that decimal by 100 to convert it into a percentage:
0.72 × 100 = 72. - 4Add the % sign to your final answer: 72%.
Enter your own part and whole in the calculator below to see the working.
Try it yourself
Pre-filled with the example — change any value.
Common mistakes to avoid
- Forgetting to multiply by 100. 0.72 is a decimal, not a percentage — it must become 72%.
- Rounding too early. Keep a few decimal places until the final step to avoid small errors adding up.
- Confusing percentage with percentage change. This formula compares a part to a whole; to compare an old value to a new one, use percentage change instead.
Tips and tricks
- Finding a percentage of a number works backward: convert the percentage to a decimal, then multiply it by the number.
- Double-check with a benchmark, such as knowing that 50% is always half.
- Once you know the percentage, the discount calculator and marks percentage calculator apply the same idea to shopping and exams.
Where you'll use it in real life
- School: working out your score on a test or assignment.
- Shopping: checking a discount or how much sales tax adds to a bill.
- Budgeting: figuring out what portion of your income went to rent or savings.
- Sports: tracking a shooting or win percentage over a season.
Quick summary
To find what percentage one number is of another, divide the part by the whole and multiply by 100. Always keep the part on top of the fraction, and don't forget the final ×100 step. Try the calculator above with your own numbers to see the full working.
Worked example
You scored 18 out of 25 on a quiz. What percentage did you get?
- 01Percentage = (18/25) × 100
- 02Percentage = 0.72 × 100
- 03Percentage = 72%
These numbers are pre-filled in the calculator above.
Frequently asked questions
How do I calculate a percentage of a number?
Convert the percentage to a decimal by dividing it by 100, then multiply it by the number. For example, 20% of 150 is (20 ÷ 100) × 150 = 30.
How do I find what percentage one number is of another?
Divide the part by the whole, then multiply by 100. If you scored 18 out of 25, that's (18 ÷ 25) × 100 = 72%.
Can a percentage be more than 100%?
Yes, when the part is bigger than the whole, such as measuring growth. For example, if a value doubles, it becomes 200% of the original.
What is 50% of a number the fast way?
50% simply means half, so divide the number by 2. There's no need for the full formula for common percentages like 50%, 25%, or 10%.
