Date interval & time-zone converter
Count Gregorian calendar dates or convert a local date and time between IANA zones. All calculation happens in your browser. The converter exposes missing and repeated local times and uses your browser’s installed time-zone data.
Calendar-day mode
The elapsed difference from April 10 to April 13 is three days. Inclusive counting returns four dates. Gregorian validation includes leap years. The mode includes weekends and holidays and does not count elapsed local-clock hours.
Time-zone mode
Enter a named IANA source and destination zone. A forward clock jump can leave no matching instant; a backward jump can produce two. The tool rejects a missing time and displays both repeated-hour candidates with UTC references.
Data and scope
Date arithmetic supports 1900–2100; conversion supports 2000–2099. Zone conversion relies on browser Intl data, which can lag IANA updates. Future rules can change. No entries are uploaded or saved, and the tool does not issue invitations or determine legal deadlines.
From the tool to the explanation
Inputs are processed in your browser. Read the related guides to understand the assumptions, worked examples and limits of a result.
Explore the complete guides ↗