Percentage Calculator
Instantly calculate "A's B%", "A is what % of B", and "what % increase" all in one place
Features
4 calculation types on one page
Forms for different uses—ratios, rates of change, and more—consolidated in one place
Automatic calculation as you type
Results appear instantly as you enter values, with no need to click an execute button
Increases and decreases labeled with words
"Increase", "decrease", or "no change" labels prevent misinterpretation
Results rounded to 2 decimal places
Raw numbers without thousand separators for easy transfer
How to use
Select the form that matches your need
Choose from 4 headings like "What is B% of A" or "A is what % of B" that fit your purpose
Enter two numbers in the input fields
Fill in the original number and percentage, or the before and after values in each form's input fields
Check the result that appears on screen
No execute button needed—results update automatically as you change inputs. Rate of change is shown with labels for increase or decrease
Use cases
Check discount amounts while shopping
Instantly see the final price for discounts like "20% off 5000 yen" before checkout
Month-over-month sales or traffic changes
Calculate the rate of change from before and after figures to use in reports
Calculate test score percentages
Convert scores like "30 out of 48" into percentages to check achievement rates
Calculate invoiced amounts with markup
Check both the amount added and subtracted to base fees at the same time
Basic knowledge
How to calculate percentage
Percentage is calculated as "amount compared ÷ base amount × 100". For example, 30 out of 48 people is 30 ÷ 48 × 100 = 62.5%. Conversely, "base amount × rate ÷ 100" gives you the amount corresponding to that percentage.
Rate of change formula
Rate of change is calculated as "(after − before) ÷ before × 100". A positive result indicates increase, negative indicates decrease. A change from 2500 to 2000 is −20%, which represents a 20% decrease.
Differences between ratio, fraction, and percentage
- Percentage：Percentage is a unit expressing a ratio where the base amount equals 100. It uses the % symbol, so 0.25 is written as 25%.
- Fraction (wa, bu, rin)：Fraction is a unit expressing a ratio where the base amount equals 10. 1 wa equals 10%, 1 bu equals 1%, and 1 rin equals 0.1%.
- Ratio：Ratio is the number itself expressing the size of the compared amount relative to the base amount, written as a decimal like 0.625 with no unit.
Safety and privacy
Runs entirely in your browser
Your input data is processed only within your browser and is never sent externally.
Processing only in your browser
Calculations is processed entirely within your browser, and input data is not sent to any server.
Communications encrypted with HTTPS
Page loading is also encrypted by TLS, and content cannot be read by third parties.
No transmission to third parties
Input content is not sent to external services such as ad networks or trackers.
No automatic saving of results
Entered numbers and input suggestions are not stored on the server.
Updates
- update #235
Added percent calculator that performs 4 types of percent calculations at once