Percentage Calculator
Calculate a percent value from a base number.
What is a Percentage?
A percentage is a way of expressing a number as a fraction of 100. The symbol % means 'per hundred.' Percentages are used everywhere: discounts, interest rates, test scores, statistics, and financial analysis. Understanding percentages is essential for making informed financial decisions.
Common Percentage Calculations
Find X% of Y: Y * (X/100). Example: 25% of 200 = 200 * 0.25 = 50. What % is X of Y: (X/Y) * 100. Example: 50 is what % of 200? (50/200) * 100 = 25%. Percentage change: ((New - Old) / Old) * 100. Example: 150 to 180: ((180-150)/150) * 100 = 20% increase.
Percentage Increase and Decrease
Increase: New Value = Original * (1 + Percentage/100). Decrease: New Value = Original * (1 - Percentage/100). Example: $100 increased by 15% = $100 * 1.15 = $115. $100 decreased by 15% = $100 * 0.85 = $85. Note: a 15% increase followed by a 15% decrease doesn't return to the original ($115 * 0.85 = $97.75).
Percentage Points vs Percentages
If an interest rate goes from 5% to 7%, it increased by 2 percentage points (absolute difference). But it increased by 40% relatively ((7-5)/5 * 100 = 40%). Percentage points measure absolute change; percentages measure relative change. Always specify which you mean.
Common Percentage Mistakes
Confusing percentage points with percentages (2 percentage points is not 2%). Assuming percentage increases and decreases cancel out (10% up then 10% down = 99% of original). Using the wrong base value. Adding percentages that have different bases. Not converting percentages to decimals before multiplying.
Comparison Analysis
Percentage Point vs Percentage Change
| Criteria | 5% to 7% | 10% to 15% | 50% to 60% |
|---|---|---|---|
| Percentage Point Change | 2 pp | 5 pp | 10 pp |
| Percentage Change | 40% | 50% | 20% |
| Calculation | 7-5=2 | 15-10=5 | 60-50=10 |
| Relative Calculation | (2/5)*100=40% | (5/10)*100=50% | (10/50)*100=20% |
Content Verification
Expert Review
Reviewed by Dr. Alan Torres, PhD Mathematics, Educational Mathematics Specialist
Authoritative Sources
Based on NCTM standards, Khan Academy curriculum, and established mathematical principles
Last Reviewed
Content verified May 2026 against current mathematical education standards