Decision tools built for clarity
Percentage Calculator
Calculate a percentage or compare how two values changed.
Choose a calculation type, enter both requested values, and calculate the result.
Methodology
Formula or transformation
Applies the selected percentage relationship to the two submitted decimal values.
Variables
- Mode
- First submitted value
- Second submitted value
Units
- Decimal number
- Percent
Rounding policy
The final percentage result is rounded to the declared result scale using half away from zero.
The selected percentage mode uses its declared reference value and direction of change.
Calculate a percentage of a value, a relative percentage, an increase, a decrease, or a percentage difference.
Reviewed sources
- NIST — Rules and style conventions for expressing values Reviewed on 2026-09-07
- U.S. Bureau of Labor Statistics — Calculating percent changes Reviewed on 2026-09-04
Formula review history
-
Initial formula and source review.
Reviewed 2026-09-02 for formula version percentage-modes-v1
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Confirmed formula identity, sources, rounding, and public disclosure.
Reviewed 2026-09-04 for formula version percentage-modes-v1
Assumptions
- Both values describe comparable quantities in the same unit.
- The selected mode determines which value is the reference value.
Limitations
- A zero reference value can make some percentage modes undefined.
- The result describes arithmetic change, not the cause or significance of that change.
Worked example
If a value rises from 80 to 100, the increase is 20 divided by the starting value of 80, which is 25%.
Frequently asked questions
Which value is the baseline?
For increase and decrease, the starting value is the baseline. Other modes follow their labels.
Why can a calculation be unavailable?
A mode that requires division cannot use a zero denominator.