<div class="nfaf-generated-content"><div class="nfaf-visual-card" style="--nfaf-accent:#481429"><div class="nfaf-visual-icon" aria-hidden="true"><svg viewBox="0 0 64 64" role="img"><circle cx="32" cy="32" r="28" fill="currentColor" opacity=".12"></circle><path d="M20 34l8 8 17-19" fill="none" stroke="currentColor" stroke-width="5" stroke-linecap="round" stroke-linejoin="round"></path></svg></div><div><strong>Number Format and Percentage Calculator</strong><span>Browser-first utility with visible inputs, outputs, and limitations.</span></div></div><p class="nfaf-lede">This tool separates display formatting from arithmetic so a rounded presentation is not confused with the underlying value.</p><p><strong>Designed for:</strong> Analysts, editors, and developers preparing readable numeric examples.</p><h2>How to use this tool</h2><p>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.</p><h2>How the result is produced</h2><p>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.</p><h2>Test examples</h2><p>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.</p><h2>Limitations</h2><p>Floating-point arithmetic, rounding, currency rules, significant figures, and negative values need domain-specific review. This is not financial, tax, or accounting advice.</p><h2>Privacy and processing</h2><p>Values are formatted and calculated in the browser and are not uploaded.</p><h2>Related guide</h2><p><a href="https://nofyi.com/percentage-change-needs-a-clear-denominator/">Percentage change needs a clear denominator</a></p><h2>Related tools in this category</h2><ul class="nfaf-related-tools"><li><a href="https://nofyi.com/tools/number-base-converter/">Number Base Converter</a><span>Enter a non-negative integer in one base and inspect its representation in the others.</span></li></ul><h2>Documentation</h2><ul><li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/NumberFormat" rel="nofollow noopener" target="_blank">https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/NumberFormat</a></li><li><a href="https://tc39.es/ecma402/" rel="nofollow noopener" target="_blank">https://tc39.es/ecma402/</a></li></ul><p class="nfaf-disclosure">This page describes the implementation shipped with the NOFYI Tool Factory. Review the interface output before using it in a production workflow.</p></div><div class="nfaf-app-slot">[nfaf_tool_app]</div>
