Using the percentage change calculator

The tool is intentionally minimal: two inputs and one primary output. That design keeps cognitive load low when you are on a call and need a number in seconds. Everything runs locally in the browser on this static build, so nothing you type leaves the page for server-side processing.

The companion line under the headline exists because signed percents confuse skimmers. Saying "decrease versus the original" reinforces the negative sign without opening a spreadsheet.

The calculator evaluates ((new − original) ÷ |original|) × 100% using JavaScript floating point, then rounds for display. Extremely large magnitudes can reflect floating noise; re-type values if something looks off.

When original is zero, the tool prints N/A. That is the same guardrail described in the step-by-step guide and the formula article.

1. Decide which real-world measurement is the original and type it first.
2. Type the new measurement after the change you care about.
3. Wait for both fields to contain valid numbers; partial input shows a waiting hint.
4. Read the headline percent and the increase or decrease line together.
5. If you see N/A, switch to absolute change or pick a nonzero baseline.

Practice with the sample pairs listed under the tool on the home page, then invent your own from worked examples.

List price 200, sale price 160. Enter 200 as original and 160 as new. The headline should read −20%, and the trend line should read decrease versus the original. If you reversed the fields, you would still see 20% magnitude but the story would mislabel the marketing narrative.