How to use this percentage calculator
Percentages show a part of a whole as a fraction of 100. This tool covers the five lookups people search for most often:
- What is X% of Y? — sales tax, tips, commissions, and discounts.
- X is what percent of Y? — grades, conversion rates, and progress toward a goal.
- Percent change — growth or decline from an old value to a new value.
- Increase / decrease by % — markups, salary raises, and markdowns.
Percentage formulas
What is X% of Y?
Result = (X ÷ 100) × Y. Example: 15% of 200 = 0.15 × 200 = 30.
X is what percent of Y?
Percent = (X ÷ Y) × 100. Example: 30 is what percent of 200? (30 ÷ 200) × 100 = 15%.
Percent change
Percent change = ((New − Old) ÷ |Old|) × 100. A rise from 80 to 100 is a 25% increase.
Increase or decrease by a percent
New value = Start × (1 ± Percent ÷ 100). A $50 item marked up 20% becomes $60; marked down 20% becomes $40.
Common percentage examples
- A $42 restaurant bill with 8% tax: 8% of 42 = $3.36 tax.
- Score 46 out of 50: 46 is 92% of 50.
- Stock from $25 to $30: ((30 − 25) ÷ 25) × 100 = 20% gain.
- Salary $4,000 raised 5%: 4000 × 1.05 = $4,200.
Why percentages matter
Retail, finance, analytics, and school grading all rely on clear percent math. Using a calculator reduces rounding mistakes when you compare offers, track KPIs, or fill forms that ask for percent values.
All math here runs locally in your browser. Nothing you type is uploaded — useful when you are checking private figures before you paste them into a spreadsheet or invoice.
Related tools
Need a monthly payment estimate? Try the loan calculator. Splitting a check? Use the tip calculator. Writing amounts on a check? Use numbers to words.