Salary up from $80,000 to $90,000 — what's the percentage increase? A $90 discount on a $300 item — what percent off is that? A score of 72 out of 100 — what percentage is it? Percentages are the most common math concept in daily life. Let's make them foolproof.
The Percentage Formula
Percentage = Part ÷ Whole × 100%
One rule covers it all: divide the part by the whole, then multiply by 100. What percent of 200 is 50? 50 ÷ 200 × 100% = 25%.
Common Use Cases
| Scenario | Formula | Example |
|---|---|---|
| Increase / decrease | (new − old) ÷ old | $80K→$90K = 12.5% up |
| Discount | discounted price ÷ original | 210÷300 = 70% = 30% off |
| Score rate | score ÷ total | 72÷100 = 72% |
| Share / proportion | part ÷ whole | budget item = 20% |
Common Percentage Mistakes
- The base is the old value: $80K→$90K is a 12.5% rise, not 11.1%
- Rise then fall doesn't cancel: +50% then −50% leaves you 25% down, not back to the start
- Don't flip discounts: "20% off" means price × 0.8, not "subtract 80%"
Reverse Calculation: Finding the Part
Sometimes you know the percentage and the whole, and need the part (part = whole × percentage). What's 20% of $5,000? 5,000 × 20% = $1,000.
Solve It Instantly with a Calculator
For "what percent", "what share", or "percentage change" problems, manual math gets confusing fast. Use the percentage calculator — enter the numbers and question type, get the answer in one click, no errors.
Pair it with the discount calculator for shopping math, and the GPA calculator for academic conversions.
Quick Mental Math
Handy shortcuts: 10% = move the decimal one place left; 5% = half of 10%; 15% = 10% + 5%. With these, most everyday conversions take seconds.
For precise results, hand it to the percentage calculator — fast, accurate, stress-free.