About

HowLong is a collection of practical time and date tools. Each page starts with the task you came to solve.

How calculations work

Calculations run in your browser. Fixed durations are kept separate from calendar dates. Working-day calculations show the dates they skip, and countdowns display the selected time zone and target date.

Accuracy and limitations

Time-zone rules come from your browser’s IANA time-zone data. Your device clock must be correct. Business-day tools do not silently apply holiday calendars. Calendar month operations clamp to month end if the same day does not exist.

Review the implementation

The calculation code, automated tests and keyword-to-page coverage are maintained in the project repository. To report a problem, use the contact page.

No account needed

You can use the tools without registration. Inputs are processed on your device. See our privacy policy for details.