Percentage Calculator
What is 15% of the bill? (Asking for a friend at a restaurant.)
About This Calculator
How It Works
This calculator handles the three most common percentage questions people actually get stuck on: finding a percentage of a number (what's 20% of $85?), calculating the percentage change between two values (how much did my rent increase?), and figuring out what percentage one number is of another (30 out of 120 — what percent is that?). Each mode uses a slightly different formula, and switching between them lets you solve problems in whatever direction the question comes from.
The Formula
P% of X = (P/100) × X. Percent change = (new-old)/old × 100. What % is A of B = (A/B) × 100.
When to Use This
Percentages come up constantly: tipping at a restaurant, calculating sale discounts, understanding a pay raise, reading nutrition labels, interpreting statistics, or comparing test scores. The 'percent change' mode is especially useful for tracking things over time — price inflation, weight changes, sales growth — where the raw numbers don't tell the full story without context.
Example
15% of $87.50 (a dinner bill) = $13.13. Tip your servers, folks. They remember.
Did You Know?
The percent sign (%) didn't appear until the 15th century — before that, people wrote 'per cento.' It slowly contracted over time. Math notation has been abbreviating itself for 600 years.