How to Calculate Percentages: A Complete Guide
Percentages are part of everyday life — from shopping discounts and salary raises to taxes and investment growth.
This guide explains how to calculate percentages quickly and accurately using proven formulas, tables, and examples.
What Is a Percentage?
A percentage expresses a number as a fraction of 100.
It represents how one quantity compares to another in parts per hundred.
For example:
- 25% means 25 out of 100 (or 0.25 as a decimal)
- 50% means half (or 0.5)
- 100% means the full value
Understanding this basic concept makes all other percentage calculations easier.
Basic Percentage Formulas
| Operation | Formula | Example | Result |
|---|---|---|---|
| Find X% of Y | (X ÷ 100) × Y | 25% of 80 | 20 |
| Find what percent A is of B | (A ÷ B) × 100 | 20 of 80 | 25% |
| Percentage increase from A to B | ((B - A) ÷ A) × 100 | 50 → 75 | 50% |
| Percentage decrease from A to B | ((A - B) ÷ A) × 100 | 100 → 80 | 20% |
Each formula above can be applied instantly using the online calculators available on this site.
Common Percentage Examples
| Scenario | Formula | Example | Result |
|---|---|---|---|
| Shopping discount | (Discount% ÷ 100) × Price | 20% off $100 | $80 |
| Tip with tax | Bill + Tax + Tip | $50 bill, 10% tip, 8% tax | $59.40 |
| Salary raise | ((New - Old) ÷ Old) × 100 | $4000 → $4500 | 12.5% |
| Investment return | ((New - Old) ÷ Old) × 100 | $1000 → $1300 | 30% |
These examples show how percentage calculations apply in real financial and everyday scenarios.
Quick Tricks for Mental Math
- 10% rule: Move the decimal one place left (10% of 250 = 25)
- 5% rule: Half of 10% (5% of 250 = 12.5)
- 1% rule: Move the decimal two places left (1% of 250 = 2.5)
- Combine rules: 15% = 10% + 5% → 25 + 12.5 = 37.5
These shortcuts help you estimate percentages quickly without using a calculator.
Common Mistakes to Avoid
- Forgetting to divide by 100 when converting a percentage to a decimal.
- Using the wrong base number when comparing two values.
- Confusing percentage increase with percentage points.
- Rounding too early — always keep at least two decimal places until the final step.
Avoiding these mistakes ensures your results remain accurate and consistent.
Final Thoughts
Understanding how to calculate percentages helps in personal finance, shopping, investing, and data analysis.
Practice using the calculators provided on this site — they are free, accurate, and mobile-friendly.
Bookmark this page so you always have a reliable reference for quick percentage calculations.