Percentage Calculator Guide: Percent Of, Change, and Increase
Calculate percentages, percent change, and what percent one number is of another—with formulas and a free percentage calculator.
Published June 6, 2026 · 2 min read
Percent means per hundred. Whether you are grading papers, measuring sales growth, or figuring a sale discount, the same three patterns appear: What is p% of N?, A is what % of B?, and What is the percent change from old to new?
This guide lists the formulas and Toolsle’s free percentage calculator.
Core formulas
| Question | Formula |
|---|---|
| p% of V | V × (p ÷ 100) |
| A is what % of B | (A ÷ B) × 100 |
| Percent change | ((new − old) ÷ old) × 100 |
Example (increase): Revenue rose from $40,000 to $46,000 → (46,000 − 40,000) ÷ 40,000 = 15% increase.
Calculate any percentage problem
Calculate percentages, percentage change, and percentage difference instantly. Four calculation modes in one free tool.
Open tool →Percentage points vs relative percent
Raising a rate from 3% to 4% is a 1 percentage point increase—but a 33% relative increase in the rate itself. News headlines mix these; know which denominator you need.
Related everyday tools
- Discount calculator — sale price after % off
- Tip calculator — gratuity as a percent of bill
- GPA calculator — weighted averages use similar math
Common mistakes
- Averaging two percentages without a common base (10% of 100 + 20% of 50 ≠ 15% overall)
- Dividing by the new value when the rubric asks for change from the original
- Double-dividing by 100 in spreadsheets (store 0.18, not 18%, in multiply cells)
Try the free percentage calculator
Pick the mode that matches your question on the percentage calculator. Enter two or three values; results update instantly in your browser.
Try the free Percentage Calculator
Calculate percentages, percentage change, and percentage difference instantly. Four calculation modes in one free tool.
Open tool →