Subtract the offset to find UTC
02The signed offset is local clock time minus UTC. Finding the corresponding UTC date and time can cross a day or year boundary.
2026-10-22T09:30:00 has no stated UTC relation. It is not a complete §5.6 date-time timestamp; do not guess a device’s local zone to interpret a protocol value.
Source for this drawing: RFC 3339 · Read RFC section 4.2 ↗
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UTC equals local time minus its numeric offset.
- A negative offset means the local clock is behind UTC: subtracting that negative amount adds time. A positive offset is subtracted.
- The numeric offset gives the relation to UTC for this instant. It does not supply a location’s daylight-saving rules or predict future offset changes.
- A complete RFC 3339 timestamp includes an offset. Systems unaware of their UTC relation and depending on synchronization with Internet systems MUST use a mechanism ensuring correct UTC synchronization; an unqualified clock is insufficient.
Each conversion is a separate example, not a moving clock or a network synchronization exchange. The conversion preserves fractional digits and changes the date when necessary. Whole-minute numeric offsets are the format’s scope; some historical offsets need conversion to a representable zone. RFC 3339 formats an instant rather than synchronizing a clock or defining a recurring local appointment.
Read the RFC section ↗