Percentage Calculator
Use these quick tools to solve the most common percentage math problems: finding a percent of a number, calculating percentage change, and adding or subtracting percentages.
1) Find X% of Y
Example: What is 15% of 240?
2) What percent is A of B?
Example: 30 is what percent of 120?
3) Percentage increase or decrease
Example: from 80 to 100 is a 25% increase.
4) Add or subtract a percentage
Example: Add 8.25% tax to $60, or subtract 20% discount from $60.
How to calculate percentage on the calculator (step-by-step)
If you use percentages in daily life—shopping discounts, tax, tips, exam scores, interest rates, and budgeting—knowing a few quick methods can save time and prevent mistakes. The good news: percentage calculations are simple once you understand the formulas behind the calculator buttons.
Below is a practical guide you can use with a phone calculator, a basic calculator, or a scientific calculator.
Core percentage formulas you should know
- X% of Y = (X ÷ 100) × Y
- What percent is A of B? = (A ÷ B) × 100
- Percentage change = ((New − Old) ÷ Old) × 100
- Add a percentage = Base × (1 + X/100)
- Subtract a percentage = Base × (1 − X/100)
Method 1: Using the % key on a standard calculator
Find a percent of a number
To find 25% of 480, enter 480 × 25%. Many calculators return 120 immediately.
Add a percentage (like tax)
To add 8% tax to 50, enter 50 + 8% on some calculators, or do 50 × 1.08 on all calculators. Result: 54.
Subtract a percentage (like a discount)
To subtract 30% from 90, do 90 × 0.70 or 90 × (1 − 0.30). Result: 63.
Method 2: If your calculator has no % button
No problem. Convert the percentage into a decimal:
- 15% = 0.15
- 7.5% = 0.075
- 125% = 1.25
Then multiply. Example: 15% of 240 = 0.15 × 240 = 36.
Common real-life examples
1) Shopping discount
A $80 item is 25% off. Discount = 80 × 0.25 = 20. Final price = 80 − 20 = $60.
2) Restaurant tip
Bill is $42, tip is 18%. Tip = 42 × 0.18 = 7.56. Total = 42 + 7.56 = $49.56.
3) Sales tax
Price is $120 and tax is 8.25%. Tax = 120 × 0.0825 = 9.90. Total = $129.90.
4) Exam score percentage
You scored 44 out of 55. Percentage = (44 ÷ 55) × 100 = 80%.
How to calculate percentage increase and decrease
Use this when prices, salaries, subscribers, or metrics change over time.
- Old value: 200
- New value: 260
Percentage change = ((260 − 200) ÷ 200) × 100 = 30%. That is a 30% increase.
If the result is negative, it is a percentage decrease.
How to find the original value before a percentage change
Sometimes you know the final value and percentage but need the starting number.
After a 20% discount, the price is $64. What was the original price?
After a 20% discount, you keep 80% of the original. So:
Original = 64 ÷ 0.80 = 80
Original price was $80.
Common mistakes to avoid
- Forgetting to divide by 100 when converting a percentage to decimal.
- Using the new value as the base in percentage change calculations (use the old/original value).
- Adding and subtracting percentages directly in multi-step problems without recalculating the base.
- Rounding too early. Keep extra decimal places until the final answer.
Quick mental math shortcuts
- 10% is just move decimal one place left (10% of 250 is 25).
- 5% is half of 10% (5% of 250 is 12.5).
- 1% is move decimal two places left (1% of 250 is 2.5).
- 15% = 10% + 5%.
Final takeaway
To calculate percentage on a calculator quickly, remember: convert percent to decimal, multiply for “percent of,” divide then multiply by 100 for “what percent,” and use old value as the base for percentage change. If you want fast answers, use the calculator at the top of this page for discounts, tax, tip, growth rates, and more.