Five Types of Percentage Calculations
Most percentage problems fall into one of five categories. A good calculator handles all of them, but knowing the formulas helps you understand what the result means:
1. Percentage of a Number
What is 15% of 200?
Result = (Percentage / 100) × Number
15% of 200 = (15/100) × 200 = 302. What Percent Is One Number of Another?
30 is what percent of 200?
Percentage = (Part / Whole) × 100
(30 / 200) × 100 = 15%3. Percentage Increase
What is 200 after a 15% increase?
New Value = Original × (1 + Percentage/100)
200 × (1 + 15/100) = 200 × 1.15 = 2304. Percentage Decrease
What is 200 after a 15% decrease?
New Value = Original × (1 − Percentage/100)
200 × (1 − 15/100) = 200 × 0.85 = 1705. Percentage Change Between Two Values
What is the percentage change from 200 to 230?
Change = ((New − Old) / |Old|) × 100
((230 − 200) / 200) × 100 = 15% increaseCommon Percentage Mistakes
- Adding percentages that don't stack additively: A 20% discount followed by another 20% discount isn't 40% off — it's 36% off (80% × 80% = 64% of original).
- Confusing percentage points with percent: Going from 10% to 15% is a 5 percentage point increase, but a 50% percent increase. These are very different numbers.
- Base confusion: "Sales are up 50% this quarter" means relative to last quarter, not some absolute number. Always know the base.
- Reversing a percentage: If price increases 25%, you need a 20% decrease to get back to the original — not 25%. The base has changed.
Real-World Uses
- Sales tax: 8% on a $50 purchase = $4 tax, $54 total.
- Discounts: 30% off a $80 item = $24 saved, $56 final price.
- Tips: 20% on a $65 meal = $13 tip, $78 total.
- Growth rates: Revenue grew from $1.2M to $1.5M = 25% growth.
- Grades: 45 out of 60 = 75%.
Calculate Percentages Instantly
Use ToolsVito's Percentage Calculator for percentage of a number, percentage change, increase/decrease, and finding original values. All calculations in your browser.