How to Calculate the Percentage of a Number
Short answer
Part = whole × (percent ÷ 100). 15% of 80 = 80 × 0.15 = 12. To find what percent one number is of another: (part ÷ whole) × 100.
This is the core percentage skill behind tips, discounts and exam scores. Practice with the percentage calculator.
Three related questions
- What is P% of N?
- N is what percent of M?
- N increased/decreased by P% is what?
Examples
- 20% of 250 = 50
- 45 is what percent of 180? 45 ÷ 180 × 100 = 25%
- Sale: see discount percentage and the discount calculator
- Restaurant: how to calculate a tip / tip calculator
Percentage increase
When comparing two values, use percentage increase between two numbers.
See also: a levels exam guide.
More worked numbers
Change one input at a time so you build intuition. Write the formula, substitute values, then confirm with the free percentage calculator. If the tool disagrees with your hand math, check units first (months vs years, percent vs decimal, inclusive ranges).
Common mistakes to avoid
- Mixing up percent and decimal forms (15% is 0.15, not 15).
- Using the wrong base when calculating a change or a reverse percentage.
- Ignoring fees, tax or daylight saving when the real-world total depends on them.
- Rounding too early in multi-step arithmetic.
How to practise
Invent three mini-problems from your own life — a bill, a grade, a trip, a loan quote — and solve them on paper before you open the calculator. Teaching the steps to someone else is one of the fastest ways to lock in the method.
Related tools on ViralScopeHub
After you finish this guide, explore the linked tools above and the related articles for neighbouring skills. Our calculators run privately in your browser with no sign-up, so you can check homework, budgets or work estimates without uploading data.
Quick reference card
Keep the short answer box at the top of this page as your cheat sheet. When a search result brought you here for a specific phrase, that box is designed to match the query with the formula first, then the examples below fill in the judgement calls.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percent divided by 100. Double-check units and confirm with the linked tool on this page before you rely on the figure for money or school decisions.
What is 17% of 90?
90 × 0.17 = 15.3. Double-check units and confirm with the linked tool on this page before you rely on the figure for money or school decisions.
How do I reverse it?
If 15.3 is 17% of a number, divide 15.3 by 0.17 to get 90. Double-check units and confirm with the linked tool on this page before you rely on the figure for money or school decisions.
Is percent the same as percentage points?
No — see our percentage increase guide for the difference. Double-check units and confirm with the linked tool on this page before you rely on the figure for money or school decisions.