What you can do here
One site for human and machine-readable time
Use the world time planner for a date-aware 24-hour comparison, the big clock for a live multi-city display, or browse individual city clocks and popular city pairs. The date section covers D-Day countdowns, days between dates, working days, and adding or subtracting days. Developers can use the same epoch and timestamp-difference rules through the JSON API.
Results are designed to be readable, copyable, and linkable. Where an input can be ambiguous, the tool asks for a date, an IANA time zone, or an explicit UTC offset instead of silently guessing.
How accuracy works
Named time zones, exact instants
Time conversions use named IANA zones such as Europe/London and America/New_York. The selected instant is converted separately for every city, so daylight-saving transitions and half-hour or quarter-hour offsets are included. City-pair pages check every day of the current year for seasonal differences and calculate the shared 09:00-17:00 working window for each pattern.
The interactive map geometry is based on timezone-boundary-builder 2026b, with Natural Earth data used for geographic context. A boundary helps choose a named zone; the calculator then resolves that zone's offset for the instant being viewed.
Limits and corrections
Time-zone rules can change
Governments can announce time-zone or daylight-saving changes with little notice, and browsers or deployed runtimes may receive those updates at different times. Map boundaries are a practical selection aid, not a statement of political or legal jurisdiction. For travel, payroll, legal deadlines, medical care, or another critical decision, verify the result with the relevant local authority.
If a city, offset, label, or calculation looks wrong, please send the page, city, date, expected result, and actual result through the Contact page. Reproducible reports make corrections much faster.