About & calculation methods

Whenfold is an independently operated collection of free tools for coordinating time and dates. It is built for people planning calls, remote work, travel and shared deadlines.

How the calculations work

Time conversion uses the time zone data available in the JavaScript runtime through Intl.DateTimeFormat. Time zones are identified by IANA names, not a permanently fixed UTC offset. The converter checks for local times that are missing or repeated during daylight-saving changes.

Date differences compare Gregorian calendar dates at UTC midnight, so a daylight-saving day is still one calendar day. ISO week numbers use Monday as the first day and the first Thursday to determine week 1. Public holidays are not applied.

Limits and corrections

Dates from 1900 to 2100 are supported. Governments can change time-zone rules; runtime data may lag those changes. Check critical travel or scheduling decisions against the relevant organiser. These tools do not calculate legal deadlines or working days.

Intl.DateTimeFormat · IANA time zone database

Business model

The tools are free. Advertising is currently disabled while provider approval and setup are completed. No paid visitor subscription is required. Advertising enquiries and corrections can be sent through our contact form.