Percentage Calculator
Use any of the tools below to solve common percentage questions instantly.
1) What is X% of Y?
2) X is what percent of Y?
3) Percentage increase or decrease
4) Add or subtract a percentage (tax, tip, discount)
Tip: Choose Add for tax/tip and Subtract for discounts.
Quick answer: percentages are parts of 100
If you are asking, “How do you figure out percentages on a calculator?”, the short answer is: convert the percentage to a decimal and multiply, or divide first and multiply second. A calculator just speeds up the arithmetic.
For example, to find 20% of 150, type: 150 × 0.20 = 30. That means 20% of 150 is 30.
The 4 most common percentage calculations
1) Find a percentage of a number
Use this when someone says “What is 15% of 80?”
- Formula: (percentage ÷ 100) × number
- Calculator steps: 15 ÷ 100 × 80
- Answer: 12
Faster equivalent: convert 15% to 0.15 and multiply: 0.15 × 80 = 12.
2) Find what percent one number is of another
Use this for questions like “30 is what percent of 120?”
- Formula: (part ÷ whole) × 100
- Calculator steps: 30 ÷ 120 × 100
- Answer: 25%
3) Find percentage increase or decrease
Use this when a value changes from old to new.
- Formula: ((new − old) ÷ old) × 100
- Example: from 80 to 100
- Calculator: (100 − 80) ÷ 80 × 100 = 25%
If the result is negative, that is a percentage decrease. If positive, it is a percentage increase.
4) Add or subtract a percentage
This is useful for tips, taxes, and discounts.
- Add percent: final = base × (1 + rate/100)
- Subtract percent: final = base × (1 − rate/100)
Example discount: 25% off $80 → 80 × (1 − 0.25) = 60.
Example tax: 8% tax on $50 → 50 × 1.08 = 54.
How to do percentages on different calculators
Basic calculator (no % key needed)
You can do all percentage math with just divide, multiply, add, and subtract. That means any phone calculator, desktop calculator, or browser calculator can handle it.
- Translate the percentage into a decimal (divide by 100).
- Use multiplication for “of”.
- Use division then multiplication for “what percent”.
- Use old/new formula for change percentages.
Calculator with a % key
Some calculators let you type numbers like 200 × 15 % and return 30 directly. Others interpret the % key differently. If results look odd, use the universal method: divide by 100 first, then continue the operation.
Common mistakes to avoid
- Forgetting to divide by 100 before multiplying.
- Swapping part and whole when finding “what percent”.
- Using the new value as the denominator in percentage change (use old value).
- Rounding too early and getting small accuracy errors.
Practice examples you can check with the calculator above
Example A: What is 18% of 250?
18 ÷ 100 × 250 = 45
Example B: 42 is what percent of 60?
42 ÷ 60 × 100 = 70%
Example C: Price went from $120 to $90
((90 − 120) ÷ 120) × 100 = −25%, so it decreased by 25%.
Example D: Add 12% tip to $37.50
37.50 × 1.12 = 42.00
Final takeaway
Figuring out percentages on a calculator is straightforward once you remember one idea: percentages are fractions out of 100. Convert to decimal, then multiply; or divide and multiply to find percent. Use the calculator above anytime you need quick, accurate results for discounts, taxes, grades, budgeting, and more.