Percentage Calculator
Use these quick formulas to calculate percentages, percentage rates, and percentage increase/decrease.
1) Find X% of Y
Example: What is 15% of 240?
2) A is what percent of B?
Example: 30 is what percent of 120?
3) Increase a number by a percentage
Example: Increase 500 by 8%.
4) Decrease a number by a percentage
Example: Decrease 500 by 8%.
How to Use Percentage on a Calculator Formula
Percentages are everywhere: discounts, taxes, tips, grades, and investment returns. A percentage is simply a part of 100. The calculator formulas are straightforward once you memorize a few patterns.
Core Percentage Formulas
- Find a percentage of a number: (percent ÷ 100) × number
- Find what percent one number is of another: (part ÷ whole) × 100
- Add a percentage: number × (1 + percent ÷ 100)
- Subtract a percentage: number × (1 - percent ÷ 100)
Step-by-Step Examples
Example 1: What is 25% of 80?
Convert 25% to decimal: 25 ÷ 100 = 0.25. Then multiply: 0.25 × 80 = 20.
Example 2: 18 is what percent of 60?
Divide part by whole: 18 ÷ 60 = 0.3. Convert to percent: 0.3 × 100 = 30%.
Example 3: Increase 200 by 12%
Multiplier is 1 + 0.12 = 1.12. Then 200 × 1.12 = 224.
Example 4: Decrease 200 by 12%
Multiplier is 1 - 0.12 = 0.88. Then 200 × 0.88 = 176.
Common Mistakes to Avoid
- Forgetting to divide by 100 before multiplying.
- Switching part and whole in the “what percent” formula.
- Using addition/subtraction directly instead of multipliers for percentage increase/decrease.
- Rounding too early in multi-step calculations.
Quick Mental Math Tips
- 10% = move decimal one place left.
- 5% = half of 10%.
- 1% = divide by 100.
- 15% = 10% + 5%.
- 25% = one-quarter of the number.
Where This Helps in Real Life
You can use these formulas to compare sale prices, compute gratuity, estimate tax, monitor grade improvements, and evaluate investment growth. With a consistent formula approach, percentage problems become fast and predictable.