Percentage Calculator
Calculate what percent one number is of another, find X percent of Y, and measure percentage increase or decrease—useful for discounts, tips, grades, and growth rates.
X% of Y
Enter values below to calculate.
Result
Calculated answer and breakdown.
Result
30
15% of 200 = 30
Quick reference for 200
Methodology and limitations
Last reviewed:
Methodology
Computes percent-of-value, what-percent comparisons, and percent increase/decrease using standard percentage formulas.
Limitations
Results are mathematical estimates; verify for financial or contractual use.
How to Calculate Percentages
Calculate what percent one number is of another, find X percent of Y, and measure percentage increase or decrease—useful for discounts, tips, grades, and growth rates.
Method used
The calculator applies the selected percentage formula for percent-of, part-over-whole percentage, or percent change.
Percent change = (new value - original value) / original value x 100
Practical example
For 15% of 200, convert 15% to 0.15 and multiply by 200 to get 30.
- Mode: X% of Y
- Percentage: 15
- Number: 200
The result shows the calculated value and a plain-language explanation of the formula used.
Assumptions
- Percent values are entered as percentages, not decimals.
- Percent change needs a nonzero original value.
- What-percent mode needs a nonzero whole value.
What this includes
- Percent of a number, what percent X is of Y, percent increase, percent decrease, and quick-reference values.
What this excludes
- Sales tax rules, discounts with item restrictions, statistical confidence intervals, and financial return assumptions.
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Frequently Asked Questions
How do I calculate X percent of Y?
Convert the percent to a decimal by dividing by 100, then multiply by the number. For example, 15% of 200 is 0.15 × 200 = 30. Use this mode for discounts, tax estimates, and tip drafts when you already know the rate. Double-check whether your problem wants the portion alone or the portion added to the original.
How do I find what percent one number is of another?
Divide the part by the whole, then multiply by 100. For example, 30 out of 200 is (30 ÷ 200) × 100 = 15%. This answers questions like “what percent of my budget is rent?” Keep the whole nonzero, and watch which value is the part versus the baseline in word problems.
How is percent change calculated?
Subtract the original value from the new value, divide by the original value, then multiply by 100. Positive results are increases; negative results are decreases. For example, 80 to 100 is a 25% increase. Percent change is undefined if the original value is zero, so pick a meaningful baseline before interpreting growth.
How do I reverse a percentage to find the original?
If you know a final amount after an increase or discount, divide by (1 ± rate as a decimal) to recover the original. For example, a $80 price after 20% off implies original = 80 ÷ 0.80 = $100. Use careful signs for markups versus markdowns, and confirm whether tax was included in the stated final.
What is the difference between percentage points and percent?
A change from 10% to 12% is a rise of 2 percentage points, but a 20% relative increase because 2 is 20% of 10. Confusing those phrases leads to wrong headlines and finance mistakes. When comparing rates, state clearly whether you mean absolute percentage points or relative percent change.