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Offset-explicit calendar arithmetic / no time-zone lookup

Make the date line visible.

Start with one local departure clock. Add the UTC offsets and elapsed duration you verified, then see the destination date and clock without letting your browser guess the time zone.

Reviewed 24 July 2026 Private tool plus 5 minute method Global arithmetic with explicit offsets
01Local departureDate, clock, origin offset
02UTC bridgeSubtract, then add duration
03Local arrivalAdd destination offset

Your evidence

Arrival Clock Calculator

Every field starts blank. Use signed offsets such as +02:00, -09:00, or +05:30. An offset is evidence for one instant, not a permanent label for a city.

01 Departure local clock
Local clock minus UTC for this exact departure instant.
02 Entered elapsed duration

Enter the duration you intend to add. The tool does not obtain a scheduled, block, airborne, connection, or door-to-door duration.

03 Destination local clock
Local clock minus UTC for the calculated arrival instant.

Do not enter a name, flight number, booking reference, ticket number, document, contact detail, or exact address. Nothing is submitted, fetched, or saved by this page.

Calculated clock

The clock is still missing evidence.

No destination arrival yet

Enter both exact UTC offsets.

Departure instant
Waiting for complete departure evidence
Arrival instant
Waiting for a complete entered duration
Calendar movement
Waiting for a complete calculation

Formula record

Departure local clock - origin offset + elapsed duration + destination offset.

Missing or invalid evidence

  • Every field is blank.

This is reader-entered calendar arithmetic. It is not a schedule, live arrival, time-zone or daylight-saving lookup, itinerary validation, prediction, recommendation, booking, or guarantee.

Method

An offset belongs to an instant.

RFC 3339 defines a numeric offset as local time minus UTC. That is why the first step subtracts the origin offset. After the entered duration is added on the UTC line, the destination offset is added to express the result on the destination local clock.

The signs matter. A departure at 18:50 with an offset of -04:00 corresponds to a later UTC clock, while a positive offset corresponds to an earlier UTC clock. Keep the sign attached to the number you verified.

Do not reuse a winter offset for a summer date, or assume one abbreviation has one global meaning. IANA records transitions because civil-time rules can vary. NIST also notes that separate jurisdictions decide these rules and can change them with little notice.

The calculator rejects -00:00. RFC 3339 uses that form when the offset is unknown. Use +00:00 only when UTC itself is the verified local reference for that instant.