Percentage Calculator (3-in-1)
Use this quick calculator to solve the most common percentage problems.
1) What is X% of Y?
2) A is what percent of B?
3) Percentage Increase or Decrease
Find how much a value changed in percentage terms.
What does percentage mean?
A percentage means “out of 100.” The word comes from the Latin phrase per centum, which literally means “for each hundred.” So when we say 45%, we mean 45 out of 100, or 45/100.
Percentages are everywhere: exam scores, discounts, tax, investment returns, loan rates, business growth, and survey results. Learning how to calculate percentages quickly helps you make better everyday decisions.
The core percentage formulas
Most percentage questions can be solved with just three formulas:
- Find part: Part = (Percentage ÷ 100) × Whole
- Find percentage: Percentage = (Part ÷ Whole) × 100
- Find percentage change: ((New − Old) ÷ Old) × 100
If you remember these three, you can solve almost any basic percentage problem.
How can we calculate percentage step by step?
1) Calculate “X% of a number”
This is the most common case. Suppose you want to know 18% of 250.
- Convert 18% to decimal: 18 ÷ 100 = 0.18
- Multiply by the whole number: 0.18 × 250 = 45
Answer: 18% of 250 is 45.
2) Calculate “A is what percent of B?”
Example: 30 is what percent of 120?
- Divide part by whole: 30 ÷ 120 = 0.25
- Multiply by 100: 0.25 × 100 = 25%
Answer: 30 is 25% of 120.
3) Calculate percentage increase or decrease
Example: Price changed from 80 to 100.
- Find the difference: 100 − 80 = 20
- Divide by original value: 20 ÷ 80 = 0.25
- Multiply by 100: 0.25 × 100 = 25%
Answer: 25% increase.
Common real-life percentage calculations
Discounts while shopping
If a shirt costs $60 and there is a 15% discount:
- Discount amount = 15% of 60 = 0.15 × 60 = $9
- Final price = 60 − 9 = $51
Tax and tip
If your restaurant bill is $80 and tip is 12%:
- Tip = 12% of 80 = $9.60
- Total = 80 + 9.60 = $89.60
Exam scores
If you got 42 marks out of 50:
- Percentage = (42 ÷ 50) × 100 = 84%
Business and finance
If revenue grows from $40,000 to $50,000:
- Growth = ((50,000 − 40,000) ÷ 40,000) × 100 = 25%
Quick mental tricks for percentage calculations
- 10% = move decimal one place left (10% of 250 = 25)
- 1% = move decimal two places left (1% of 250 = 2.5)
- 5% = half of 10% (5% of 250 = 12.5)
- 25% = divide by 4
- 50% = divide by 2
- 75% = 50% + 25%
These shortcuts are very useful for shopping, budgeting, and quick checks without a calculator.
Common mistakes to avoid
- For percentage change, divide by the old/original value, not the new value.
- Don’t forget to multiply by 100 when converting from decimal to percentage.
- Check if the question asks for final amount or just percentage amount.
- Use signs correctly: negative change means decrease, positive means increase.
Practice questions
- What is 35% of 480?
- 72 is what percent of 90?
- A value rises from 200 to 260. What is the percentage increase?
- A price falls from 150 to 120. What is the percentage decrease?
Try solving these with the formulas above, then verify with the calculator at the top.
Final thoughts
If you ever ask, “How can we calculate percentage?” remember this simple plan: identify part, whole, and change; choose the right formula; compute carefully. With regular practice, percentage calculations become fast and automatic.