Number Format and Percentage Calculator
This tool separates display formatting from arithmetic so a rounded presentation is not confused with the underlying value.
Format numbers and calculate percentage change
Enter a value, locale, decimal places, and optional old/new values for a percentage comparison.
Processing mode: browser-only for this tool. The interface does not require a server upload to perform its transformation.
Start with a focused browser tool
This tool separates display formatting from arithmetic so a rounded presentation is not confused with the underlying value.
Designed for: Analysts, editors, and developers preparing readable numeric examples.
How to use this tool
Enter a number and choose decimal places and locale. Optionally enter old and new values to calculate absolute change and percentage change. Interpret the output with the units and denominator in mind.
How the result is produced
The browser uses Intl.NumberFormat for display and arithmetic in JavaScript number values. The percentage formula is `(new – old) / old * 100` when the old value is nonzero.
Test examples
A change from 100 to 110 is +10 and +10%. A change from 0 cannot produce a normal percentage because the denominator is zero; the tool reports that instead of inventing a value.
Limitations
Floating-point arithmetic, rounding, currency rules, significant figures, and negative values need domain-specific review. This is not financial, tax, or accounting advice.
Privacy and processing
Values are formatted and calculated in the browser and are not uploaded.
Related guide
Percentage change needs a clear denominator
Related tools in this category
Documentation
- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/NumberFormat
- https://tc39.es/ecma402/
This page describes the implementation shipped with the NOFYI Tool Factory. Review the interface output before using it in a production workflow.