Percentage Calculator

How the percentage calculator works

A percentage is a fraction with 100 as the denominator. "Percent" means "per hundred", so 15% is 15 out of every 100, or 0.15 as a decimal. Every percentage problem reduces to one of three questions, and this calculator handles all of them plus percent change and reverse percentages.

The three basic formulas

Common percentage shortcuts

10% of a number is the number with the decimal moved one place left. 5% is half of that. 1% moves the decimal two places. Combine them: 15% of 80 is 8 (10%) plus 4 (5%) = 12. 20% is 10% doubled. 25% is a quarter, and 50% is half.

Percent increase and decrease

To increase a value by a percentage, multiply by (1 + rate). To decrease, multiply by (1 - rate). A 20% discount on $60 is 60 x 0.8 = $48. To undo a percentage change, divide by the same factor instead of subtracting the percent: $48 / 0.8 = $60, whereas adding 20% back to $48 gives $57.60, which is wrong.

Worked percentage examples

Start with a percentage of 100 to see the calculation step by step, then follow the nearby amounts to compare other numbers.

• 1% of 100
• 2% of 100
• 3% of 100
• 4% of 100
• 5% of 100
• 6% of 100
• 7% of 100
• 8% of 100
• 9% of 100
• 10% of 100
• 12% of 100
• 15% of 100
• 18% of 100
• 20% of 100
• 25% of 100
• 30% of 100
• 35% of 100
• 40% of 100
• 45% of 100
• 50% of 100
• 60% of 100
• 70% of 100
• 75% of 100
• 80% of 100
• 90% of 100