Five calculators in one
Percentages come up everywhere: exam results, shopping discounts, pay rises, tax, statistics in the news. Most questions fall into a handful of types, so this percentage calculator has a separate tab for each, with its own clearly labeled boxes. Every answer comes with the formula and the working, so you can check it or copy the steps into homework.
The formulas
1. What is X% of Y?
Result = (X ÷ 100) × Y
Example: 20% of 350 = 0.2 × 350 = 70. Use this for tips, commission, or a share of a total.
2. X is what percent of Y?
Percentage = (X ÷ Y) × 100
Example: 42 out of 60 = 0.7 × 100 = 70%. Use this to see what share one amount is of another.
3. Percentage increase or decrease
Change % = ((New − Old) ÷ Old) × 100
Example: a price going from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25% increase. A positive answer is an increase and a negative answer is a decrease. The starting value cannot be zero, because a change from zero has no percentage.
4. Marks percentage
Percentage = (Obtained marks ÷ Total marks) × 100
Example: 387 out of 450 = 86%. The calculator checks that obtained marks are not more than the total.
5. Add or subtract a percentage
Add: Result = Y + (X% of Y). Subtract: Result = Y − (X% of Y).
Example: adding 17% tax to 120 gives 120 + 20.4 = 140.4. Taking 30% off 80 gives 80 − 24 = 56.
Everyday examples
- Shopping: a jacket costs 80 and is 25% off. Use “Add / subtract %”: 80 − 20 = 60.
- Tips: a 12% tip on a bill of 45. Use “X% of Y”: 45 × 0.12 = 5.4.
- Pay rise: a salary goes from 2,000 to 2,150 a month. Use “% change”: (2,150 − 2,000) ÷ 2,000 × 100 = 7.5%.
- Exam results: 68 out of 80 marks. Use “Marks %”: 68 ÷ 80 × 100 = 85%.
- Budgeting: rent of 700 from an income of 2,500. Use “X is what % of Y”: 700 ÷ 2,500 × 100 = 28%.
- Prices with tax: a price of 50 before 8% sales tax. Use “Add / subtract %” with Add: 50 + 4 = 54.
Common mistakes to avoid
- Percentage points vs percent. If an interest rate goes from 4% to 5%, it rose by 1 percentage point, which is a 25% increase.
- Reversing a discount. Taking 20% off and then adding 20% back does not return to the original price: 100 becomes 80, and 80 plus 20% is 96.
- Using the wrong base. Percentage change is always measured against the starting value.
- Marks and weightings. If a course weights exams differently, a simple marks percentage may not match your official grade. Check your institution’s rules.
For students
The “Marks %” tab is handy after exams, and the step-by-step working helps when a teacher asks you to show your method. If your university reports grades as a GPA or CGPA, the GPA Calculator and CGPA Calculator work out credit-weighted averages, and the CGPA page includes a converter to percentage.
Checking your own working
If you are practicing for a test, do the calculation on paper first, then type the same numbers here and compare each line of the working with yours. When the answers differ, the step where they split usually shows exactly where the mistake happened, such as dividing by the wrong number or forgetting to multiply by 100.
Sharing and privacy
The page address keeps the tab and numbers you entered, so you can bookmark a calculation or send it to someone. The calculations run in your browser; your numbers are not sent to a server.
Works on any device
The calculator works on phones, tablets and computers in any up-to-date browser. On phones, the number boxes open a numeric keypad. No app or sign-up is needed.
For other everyday calculations, try the Age Calculator or the BMI Calculator.