Percentage Change Calculator

What this tool calculates

Percentage Change Calculator is designed to give a direct answer from the values entered above. The main inputs on this page are Old value, New value. The result is intended to be readable immediately, with the explanation below available when you need to verify the method.

Method and calculation basis

For “X% of Y”, the method is Y × X ÷ 100. Percentage increase adds that amount to the starting value; percentage decrease subtracts it. Reverse-percentage calculations require division by the remaining or increased percentage rather than simply subtracting the rate.

Worked examples

Understanding the result

The output should be read in the units shown beside the result. If you are comparing alternatives, keep all unchanged assumptions identical and alter one input at a time. That makes it easier to see which value is responsible for the difference.

Assumptions, edge cases and accuracy

Time zones, daylight-saving transitions and local holidays can change calendar results. Check the zone and holiday assumptions when they matter.

Sources and methodology

• IANA Time Zone Database — Time-zone and daylight-saving rules where applicable
• ISO 8601 — Date and time representation conventions

Method reviewed for Instant Solvers V10.0 · October 2026. If you find a calculation or explanation that needs correcting, use the site Contact page and include the tool URL and the values you entered.