CHAST to Zulu overview
Primary routeThe time difference between CHAST and Zulu is exactly 12 hours and 45 minutes. Zulu is behind CHAST. For practical purposes: when it is noon (12:00) in CHAST, the time in Zulu is 23:15. When it is midnight (00:00) in CHAST, Zulu reads 11:15.
Common paired routes: Zulu to CHAST , PHOT to Zulu , and TOT to Zulu .
CHAST
UTC+12:45
Chatham Standard Time
Zulu
UTC+00:00
Zulu Time (UTC)
Operational use cases
Financial trading desks operating in New Zealand (Chatham Islands) must convert market open/close times to Zulu for counterpart coordination.
Supply chain managers use CHAST-to-Zulu conversions to align shipment tracking across Worldwide (Aviation, Military, Maritime) warehouses.
All NOTAM (Notice to Airmen) publications use Zulu time; pilots departing from Worldwide (Aviation, Military, Maritime) must convert local Zulu departure times to file flight plans.
ATC (Air Traffic Control) clearances reference Zulu exclusively—ground crew in Zulu zones decode these for gate scheduling.
Operations orders (OPORDs) specify H-hour in Zulu; ground units in Zulu territory translate these to synchronize movement.
Joint multinational exercises spanning Oceania and Worldwide use Zulu as the common reference for deconfliction.
Technical details
UTC offset explanation
Chatham Standard Time (CHAST) operates at a fixed offset of UTC+12:45. Zulu Time (UTC) (Zulu) maintains an offset of UTC+00:00. The net difference between these two zones is 12 hours and 45 minutes—meaning Zulu is behind CHAST by this amount. When converting, you subtract 12 hours and 45 minutes to get the equivalent Zulu reading.
Daylight saving behavior
Zulu Time (UTC) does not observe daylight saving time. The offset of UTC+00:00 remains constant year-round. This simplifies conversion calculations since no seasonal adjustments are necessary. However, if CHAST switches to CHADT during summer, the effective difference between the two zones may shift by one hour seasonally.
Additional notes
In the NATO military time zone system, CHAST is designated by the letter "—" and Zulu corresponds to "Z". These single-letter codes appear in Date Time Group (DTG) formatted messages used across all NATO member forces.
Zulu Time (UTC) is the civil time standard for approximately Worldwide (Aviation, Military, Maritime). Major cities operating on Zulu include business, aviation, and governmental hubs that require constant coordination with UTC-referenced systems.
Cloud infrastructure providers (AWS, Azure, GCP) log events in UTC/Zulu by default. Engineers troubleshooting incidents in Zulu regions must convert log timestamps to correlate with local observations. A 12 hours and 45 minutes mental adjustment is required for every log entry.
Everything you need to know
CHAST to Zulu operational conversion
CHAST is twelve hours forty-five minutes ahead of Zulu time. A 13:05 CHAST Tuuta Airport update is 00:20Z, while 12:30 CHAST is 23:45Z on the previous UTC date.
CHAST and Zulu time relationship
Chatham Islands standard-time schedules use local time for ground coordination, but the operational reference becomes Zulu after applying the fixed offset below.
New island day, prior UTC date
Morning island operations
UTC date boundary
Evening mainland connection review
Convert CHAST to Zulu without losing the date
Confirm the source abbreviation
Verify the timestamp is actually labeled CHAST. Similar nearby zones can share geography but not the same UTC offset.
Apply the offset
Subtract 12 hours 45 minutes from CHAST to get Zulu. For reverse checks, use this companion rule: Zulu to CHAST: add 12 hours 45 minutes and adjust the local date.
Audit the calendar date
The Zulu date changes at 12:45 CHAST. Local times from 00:00 through 12:44 convert to the previous UTC calendar date. Mark the result with a trailing Z so downstream users know it is UTC.
CHAST to Zulu examples for operational schedules
NZCI weather and runway condition check
Air Chathams movement update to mainland coordination
Late local maintenance record
24-hour CHAST to Zulu conversion table
This table uses the rare UTC+12:45 Chatham standard offset. Watch the 45-minute boundary: 12:44 CHAST is still previous-day UTC, while 12:45 CHAST is 00:00Z.
| CHAST local time | Zulu time | Operational context |
|---|---|---|
| 00:00 CHASTCurrent hour | 11:15Z (Prev. Day) | Local midnight is 11:15Z on the previous UTC date. |
| 01:00 CHASTCurrent hour | 12:15Z (Prev. Day) | Local midnight is 11:15Z on the previous UTC date. |
| 02:00 CHASTCurrent hour | 13:15Z (Prev. Day) | Local midnight is 11:15Z on the previous UTC date. |
| 03:00 CHASTCurrent hour | 14:15Z (Prev. Day) | Early island weather observations and ferry-air link checks. |
| 04:00 CHASTCurrent hour | 15:15Z (Prev. Day) | Early island weather observations and ferry-air link checks. |
| 05:00 CHASTCurrent hour | 16:15Z (Prev. Day) | Early island weather observations and ferry-air link checks. |
| 06:00 CHASTCurrent hour | 17:15Z (Prev. Day) | Morning Tuuta Airport readiness, still previous-day UTC. |
| 07:00 CHASTCurrent hour | 18:15Z (Prev. Day) | Morning Tuuta Airport readiness, still previous-day UTC. |
| 08:00 CHASTCurrent hour | 19:15Z (Prev. Day) | Morning Tuuta Airport readiness, still previous-day UTC. |
| 09:00 CHASTCurrent hour | 20:15Z (Prev. Day) | Late morning approaches the 12:45 UTC date boundary. |
| 10:00 CHASTCurrent hour | 21:15Z (Prev. Day) | Late morning approaches the 12:45 UTC date boundary. |
| 11:00 CHASTCurrent hour | 22:15Z (Prev. Day) | Late morning approaches the 12:45 UTC date boundary. |
| 12:00 CHASTCurrent hour | 23:15Z (Prev. Day) | UTC date changes at 12:45 CHAST. |
| 13:00 CHASTCurrent hour | 00:15Z | UTC date changes at 12:45 CHAST. |
| 14:00 CHASTCurrent hour | 01:15Z | UTC date changes at 12:45 CHAST. |
| 15:00 CHASTCurrent hour | 02:15Z | Afternoon mainland coordination and passenger movement. |
| 16:00 CHASTCurrent hour | 03:15Z | Afternoon mainland coordination and passenger movement. |
| 17:00 CHASTCurrent hour | 04:15Z | Afternoon mainland coordination and passenger movement. |
| 18:00 CHASTCurrent hour | 05:15Z | Evening maintenance and remote communications. |
| 19:00 CHASTCurrent hour | 06:15Z | Evening maintenance and remote communications. |
| 20:00 CHASTCurrent hour | 07:15Z | Evening maintenance and remote communications. |
| 21:00 CHASTCurrent hour | 08:15Z | Late local records stay same-date UTC after rollover. |
| 22:00 CHASTCurrent hour | 09:15Z | Late local records stay same-date UTC after rollover. |
| 23:00 CHASTCurrent hour | 10:15Z | Late local records stay same-date UTC after rollover. |
Where CHAST to Zulu conversion matters
Remote island aviation
Tuuta Airport schedules must reconcile local community time with Zulu weather validity, NOTAM references, and mainland dispatch systems.
Fractional offset logging
The 45-minute offset is easy to mishandle in spreadsheets and manual logs; every CHAST conversion needs both hour and minute arithmetic.
Mainland New Zealand coordination
Chatham is 45 minutes ahead of mainland New Zealand in both standard and daylight seasons, so shared itineraries need explicit labels.
Offset, DST, and scheduling notes
CHAST is the standard-time offset for the Chatham Islands. During the New Zealand daylight-saving season, Chatham Islands use CHADT at UTC+13:45 instead.
CHAST is not NZST
CHAST and NZST are close but not interchangeable. A Chatham timestamp is 45 minutes ahead of mainland standard time.
The rollover is fractional
Unlike whole-hour offsets, the UTC date boundary occurs at 12:45 local. Times such as 12:30 CHAST are still previous-day UTC.
Operational mistakes to avoid
Dropping the 45 minutes
Subtracting only 12 hours turns 13:05 CHAST into 01:05Z instead of the correct 00:20Z.
Using CHADT outside daylight time
CHADT is one hour ahead of CHAST. Applying CHADT math to a standard-time record makes the UTC result one hour early.
Assuming all New Zealand uses one clock
Mainland airports and Chatham Islands schedules are separated by 45 minutes, so airport code and abbreviation both matter.
Frequently asked questions
What is CHAST and how does it relate to Zulu time?
CHAST stands for Chatham Standard Time, the official winter time of the Chatham Islands — a remote New Zealand territory some 800 km east of Christchurch — set at UTC+12:45 (twelve hours and forty-five minutes ahead of Zulu/UTC). To convert CHAST to Zulu, subtract 12 hours and 45 minutes from the local reading.
Related route: FJT to Zulu.
How do I convert CHAST to Zulu time?
Subtract 12 hours first, then subtract 45 minutes. If the minutes go negative, borrow an hour: for example, 13:00 CHAST − 12:00 = 01:00, then 01:00 − 0:45 = 00:15Z. For 12:30 CHAST: 12:30 − 12:00 = 00:30, then 00:30 − 0:45 = borrow → 23:45Z (previous Zulu day).
Related route: Zulu Time Now.
Why does Chatham Islands use UTC+12:45 — one of the rarest offsets on Earth?
The Chatham Islands sit at approximately 176°W longitude, placing them close to the International Date Line. New Zealand selected UTC+12:45 in the 1950s to keep Chatham on the same calendar date as mainland NZ while still reflecting its more easterly solar position with a 45-minute advance. Chatham thus shares the rare distinction of a 45-minute UTC offset with Nepal Time (NPT, UTC+5:45) — the only two 45-minute offsets in routine civilian use worldwide.
Does CHAST have a NATO military time zone letter?
No. UTC+12:45 falls between NATO letters Mike (M, UTC+12) and a hypothetical extension beyond M — no standard letter exists for this fractional offset. Military communications affecting the Chatham Islands, while rare, default entirely to Zulu time.
At what CHAST time does the Zulu date roll over?
The Zulu calendar date rolls over at 12:45 CHAST. Any CHAST time between midnight and 12:44 corresponds to the previous Zulu date; at exactly 12:45 CHAST, Zulu reaches 00:00Z.
What is aviation like on the Chatham Islands under CHAST?
Tuuta Airport (NZCI) on Chatham Island is served by Air Chathams, operating Convair 580 turboprops on scheduled routes to Wellington and Christchurch. The airport has a sealed runway but no instrument landing system, and approaches depend on weather windows. All flight plans and NOTAM coordination with Airways New Zealand reference Zulu time; CHAST appears only on the local timetable. The remote location — roughly 800 km offshore — means any weather delay requires CHAST-to-Zulu conversion to assess ATC slot expiry times accurately.
Does the Chatham Islands observe daylight saving time?
Yes. Chatham Islands advances to CHADT (UTC+13:45) during New Zealand summer — from the last Sunday of September to the first Sunday of April — matching the mainland's DST cycle. At UTC+13:45, Chatham reaches the second-most-advanced civil UTC offset on Earth, surpassed only by Kiribati's Line Islands (UTC+14).
How does CHAST relate to NZST and NZDT?
CHAST (UTC+12:45) is always 45 minutes ahead of NZST (UTC+12) in winter, and CHADT (UTC+13:45) is always 45 minutes ahead of NZDT (UTC+13) in summer. This constant 45-minute lead is preserved through both seasons, meaning Chatham residents see sunrise, noon, and sunset 45 minutes earlier than mainland New Zealanders on the same calendar date.
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