Whether you’re calculating a restaurant tip, figuring out a discount, checking credit utilization, understanding interest rates, or tracking a savings goal — percentage math appears everywhere. Here are the five most useful percentage calculations and how to do them.
The Three Core Percentage Formulas
Every percentage problem is a variation of one formula: Part = Percentage × Whole. Rearranged:
- Find the percentage: Percentage = Part ÷ Whole × 100
- Find the part: Part = Percentage ÷ 100 × Whole
- Find the whole: Whole = Part ÷ (Percentage ÷ 100)
Or skip the formula and use our free percentage calculator — it handles all three in separate tabs.
Use Case 1 — Restaurant Tips
Quick mental math for a 20% tip on any bill: move the decimal one place left (divide by 10 for 10%), then double it. $85 bill → $8.50 → $17. For 15%: find 10%, then add half. $85 → $8.50 + $4.25 = $12.75.
Use Case 2 — Sale Discounts
A $120 jacket at 35% off: 120 × 0.35 = $42 discount → final price $78. Quick shortcut: 35% off = 65% of original. 120 × 0.65 = $78.
Use Case 3 — Credit Card Utilization
If you have $2,400 in balances across cards with a $10,000 combined limit: 2400 ÷ 10000 × 100 = 24% utilization. Under 30% is the target for good credit scores.
Use Case 4 — Investment Returns
Your portfolio was worth $18,000 last year. Now it’s $21,500. Percentage gain: (21500 – 18000) ÷ 18000 × 100 = 19.4% return. Our ROI calculator handles this automatically.
Use Case 5 — Pay Raise Comparison
You currently earn $58,000. A new job offers $67,000. Percentage increase: (67000 – 58000) ÷ 58000 × 100 = 15.5% raise. Our percentage change calculator solves these in one click.
A percentage point is an absolute difference between two percentages. If interest rates go from 3% to 5%, that’s a 2 percentage point increase — but it’s a 66.7% relative increase. Finance often confuses these, leading to misinterpretation.
If a price after a 20% discount is $80, what was the original? Divide by (1 – 0.20) = divide by 0.80. $80 ÷ 0.80 = $100. Use our percentage calculator’s “Find Original Value” tab for this.