Percentage Calculator
Use this tool to solve the three most common percentage questions quickly.
Quick answer: the core percentage formulas
If you are asking, “how can I calculate percentage?”, start with these three formulas. Most percentage problems in school, work, budgeting, and shopping use one of them.
- What is X% of Y? → (X ÷ 100) × Y
- X is what percent of Y? → (X ÷ Y) × 100
- Percentage change from old to new → ((New − Old) ÷ Old) × 100
That is the whole system. Once you identify the question type, you can plug in numbers and solve confidently.
How to calculate percentage step by step
1) Find a percentage of a number
Example: What is 15% of 240?
- Convert 15% to decimal: 0.15
- Multiply by 240: 0.15 × 240 = 36
Answer: 15% of 240 is 36.
2) Find what percent one number is of another
Example: 18 is what percent of 60?
- Divide: 18 ÷ 60 = 0.3
- Convert to percent: 0.3 × 100 = 30%
Answer: 18 is 30% of 60.
3) Find percentage increase or decrease
Example: A price goes from $50 to $65.
- Difference: 65 − 50 = 15
- Divide by original value: 15 ÷ 50 = 0.3
- Convert to percent: 0.3 × 100 = 30%
Answer: 30% increase. If the new value is lower than the old value, the result is a percentage decrease.
Real-life percentage examples
Shopping discounts
If an item costs $80 and is 25% off:
- Discount amount = 25% of 80 = 20
- Final price = 80 − 20 = $60
Tips at restaurants
For a $45 bill and a 20% tip:
- Tip = 0.20 × 45 = $9
- Total = 45 + 9 = $54
Test scores
You got 42 correct out of 50 questions:
- 42 ÷ 50 = 0.84
- 0.84 × 100 = 84%
Budget and savings
If your monthly income is $4,000 and you save $600:
- 600 ÷ 4,000 = 0.15
- 0.15 × 100 = 15%
You are saving 15% of your income.
Common mistakes to avoid
- Forgetting to divide by 100 when converting a percent to decimal.
- Using the wrong base number (for percentage change, always divide by the original value).
- Mixing increase vs decrease signs when interpreting results.
- Dividing by zero (if the whole/original value is 0, percentage comparison is undefined).
Percentage shortcuts for mental math
- 10% = move decimal one place left (10% of 250 = 25).
- 5% = half of 10% (5% of 250 = 12.5).
- 1% = divide by 100 (1% of 250 = 2.5).
- 20% = double 10%.
- 25% = one quarter.
- 50% = half.
These shortcuts make discounts, tax checks, and tip estimates much faster.
Final takeaway
When you ask “how can I calculate percentage?”, the key is identifying the type of problem first: percentage of a number, part-to-whole percent, or percentage change. Use the calculator above for instant results, then practice with daily examples like shopping, budgeting, and score tracking. In just a short time, percentage math becomes second nature.