Percentage Change Calculator
How Percentage Calculations Work
Percentages express a number as a fraction of 100. They're used everywhere: discounts, tax rates, tip amounts, grade scores, growth rates, and financial returns. The key is knowing which type of percentage you're calculating — percentage of a value, percentage change, or percentage difference — because each uses a different formula.
The Core Formulas
- X% of Y: (X / 100) × Y — Example: 20% of $85 = $17
- What % is X of Y: (X / Y) × 100 — Example: 17 is what % of 85? = 20%
- Percentage change: ((New − Old) / Old) × 100 — Example: from $80 to $100 = +25%
- Percentage difference: |A − B| / ((A + B) / 2) × 100 — symmetric comparison
- Percentage off (discount): Original price × (1 − discount rate) — Example: $80 at 25% off = $60
How to Use This Calculator
- Enter the values you want to compare or calculate
- Select the type of percentage calculation if prompted
- Click Calculate for your result and the step-by-step working
Common Mistakes
Percentage increase vs. percentage points: A rate going from 5% to 8% is a 3 percentage point increase, but a 60% percentage increase. These are not the same thing, and confusing them is extremely common in news coverage.
Percentage off vs. percentage of original: "30% off $200" = $140 (you pay 70% of $200). "Pay 30% of $200" = $60. Read the phrasing carefully.