Percentage Calculator
Perform percentage calculations easily and quickly. Calculate A's B%, compare what percent A is of B, calculate increase/decrease rates, and find values after percentage changes in real-time.
Result
A's B%
150
Result
A is of B
15%
Result
Increase Rate
15%
Change Amount
150
Result
Final Value
1150
Change Amount
150
Complete Percentage Calculation Guide (2025)
01
What is a Percentage?
A percentage (%) is a ratio based on 100. "Percent" comes from Latin "per centum" meaning "per hundred". For example, 50% means 50 out of 100, or half. Percentages are widely used: discounts (30% off), test scores (85/100 = 85%), interest rates (3% annual interest), growth rates (10% year-over-year growth). The basic formula is (part/whole) × 100 = percentage.
02
Calculating A's B% (Basic Percentage)
Calculating A's B% is the most basic percentage calculation. The formula is A × (B/100). Real-life examples: Shopping discount: 20% off a $100 item is $100 × (20/100) = $20 off, final price $80. Tax calculation: 15% income tax on $50,000 is $50,000 × (15/100) = $7,500. Tip calculation: 10% tip on $50 meal is $50 × (10/100) = $5. Bank interest: 3% annual interest on $100,000 yields $100,000 × (3/100) = $3,000 after one year.
03
Calculating What % A is of B (Ratio Comparison)
The formula for what % A is of B is (A/B) × 100. Used to compare two values. Test score: 85 out of 100 is (85/100) × 100 = 85%. 90 out of 120 is (90/120) × 100 = 75%. Goal achievement: $700,000 of $1,000,000 sales target is (700,000/1,000,000) × 100 = 70% achieved. Market share: $5 billion revenue in $50 billion market is (5/50) × 100 = 10% market share.
04
Calculating Increase and Decrease Rates
The formula for increase or decrease rate is ((After - Before) / Before) × 100. Positive results indicate increase, negative indicate decrease. Price increase: Ramen price from $0.80 to $0.92 is ((0.92-0.80)/0.80) × 100 = 15% increase. Salary raise: $3,000 to $3,300 is ((3,300-3,000)/3,000) × 100 = 10% raise. Weight loss: 80kg to 72kg is ((72-80)/80) × 100 = -10%, or 10% decrease.
05
Calculating Value After Percentage Change
Calculate the value after a percentage increase or decrease. Increase formula: Original × (1 + Percent/100). Decrease formula: Original × (1 - Percent/100). Price increase: $100 item with 20% increase is $100 × (1 + 20/100) = $100 × 1.2 = $120. Discount price: $50 item with 30% discount is $50 × (1 - 30/100) = $50 × 0.7 = $35.
06
Sequential Percentage and Compound Interest
When applying percentages sequentially, apply each to the previous result. Important: 10% increase then 10% decrease does not return to original value. $100 + 10% = $110, $110 - 10% = $99. Sequential discounts: $100 item with 20% discount then 10% discount: first discount = $80, second discount = $72 (total 28%, not 30%). Compound interest: $100,000 at 5% for 3 years = $100,000 × 1.05 × 1.05 × 1.05 = $115,762.50.