Uses for the Percentage Calculator
Finance & Shopping
- Calculating discounts during sales (e.g. 20% off).
- Determining solutions for tips at restaurants (15%, 20%).
- Computing sales tax or VAT.
- Analyzing inflation price changes in 2026.
Education & Analysis
- Calculating test scores and grades.
- Measuring growth rates in business or statistics.
- Comparing old vs. new values.
- Solving complex math problems with step-by-step logic.
Percentage Formulas Explained (2026)
1. Percentage of a Number Formula
To find out what percentage X is of Y, use this formula:
Example: What percent of 50 is 20?
(20 ÷ 50) = 0.4
0.4 × 100 = 40%
2. Percentage Change Formula
Use this to calculate the change between an Old Value and a New Value:
Example: Price went from $100 to $120.
($120 - $100) = $20
($20 ÷ $100) = 0.2
0.2 × 100 = 20% Increase
3. Percentage Increase/Decrease Formula
To add a percentage to a number (increase) or subtract it (decrease):
Decrease: Value × (1 - P%)
Example: Increase 200 by 10%.
200 × (1 + 0.10) = 200 × 1.10 = 220
Common Percentage Examples
Here are quick reference examples for common percentage calculations:
| Original Value | Percentage | Result | Calculation |
|---|---|---|---|
| $100 | 10% | $10 | 100 × 0.10 |
| $100 | 20% | $20 | 100 × 0.20 |
| $100 | 25% | $25 | 100 × 0.25 |
| $200 | 15% | $30 | 200 × 0.15 |
| $50 | 18% (tip) | $9 | 50 × 0.18 |
| $1,000 | 8% (tax) | $80 | 1,000 × 0.08 |
Frequently Asked Questions
How do I calculate what percent X is of Y?
To find what percent X is of Y, divide X by Y and multiply by 100. Formula: (X / Y) × 100%. Example: 20 is what percent of 50? (20 / 50) = 0.4 × 100 = 40%.
How do I calculate percentage change?
Subtract the old value from the new value, then divide by the old value and multiply by 100. Formula: ((New - Old) / Old) × 100%. If the result is positive, it's an increase; if negative, it's a decrease.
How do I calculate 20% of a number?
To find 20% of a number, multiply the number by 0.20. For example, 20% of 150 is 150 × 0.20 = 30.
What is the formula for percentage increase?
The formula is: New Value = Original Value × (1 + Percentage/100). For a 10% increase on 50: 50 × (1 + 0.10) = 55.
How to calculate percentage without a calculator?
To find 10% of a number using mental math, simply move the decimal point one place to the left. For example, 10% of 250 is 25. To find 20%, just double that result (50). For 1%, move the decimal two places to the left.
What is 15% as a decimal?
15% is equal to 0.15. To convert any percentage to a decimal, divide by 100 or move the decimal point two places to the left.
How do I calculate a discount?
To calculate a discount, multiply the original price by the discount percentage (as a decimal) to find the money saved. Subtract this amount from the original price to get the final sale price.
Is percentage change the same as percentage difference?
Not exactly. Percentage change usually refers to the change over time for a single variable (Old vs New). Percentage difference compares two values where neither is necessarily the 'original' or 'reference', often using the average of the two as the denominator.