Percentage Calculator
Percentages answer three everyday questions: taking a portion of something (tips, discounts, taxes), expressing one number as a share of another (test scores, market share), and measuring change between two values (price moves, growth rates). Pick the mode that matches your question.
15% of 200
30
Calculation: 15 ÷ 100 × 200 = 30
How the Percentage Calculator works
The calculation follows the standard method used across the US — no shortcuts, no hidden assumptions. Here is exactly what happens behind the scenes:
Formula
portion = percent ÷ 100 × whole; change % = (new − old) ÷ old × 100
- Percent of: multiply the whole by the percent divided by 100.
- Is what percent: divide the part by the whole and multiply by 100.
- Percent change: subtract the old value from the new, divide by the old value, multiply by 100.
Frequently Asked Questions
How do I calculate a tip or sales discount quickly?
Move the decimal point: 10% of $48.50 is $4.85. Double it for 20%. For a 15% restaurant tip, take 10% plus half of that. The “X% of Y” tab confirms any amount instantly.
What is the difference between percent change and percent difference?
Percent change compares a new value to its starting point and keeps direction (increase/decrease). Percent difference compares two independent values against their average and is directionless.
Why can percent decrease exceed 100%?
A drop from 200 to 50 is a 75% decrease, but drops larger than the starting value itself would give results beyond −100%, which simply means the new value went below zero — check your inputs if values must stay positive.