Zulu is UTC with a letter after it. Type 0800Z and read the same instant as your local time, the 12-hour clock, military time, ISO 8601 and Unix.
Zulu time is Coordinated Universal Time written with the suffix Z, spoken "Zulu" from the NATO phonetic alphabet for the letter of the zero-offset time zone. 0800Z is eight in the morning in UTC — not in your kitchen, unless you happen to live on the prime meridian in winter. Aviation, the military, satellite operations and most incident logs run on it for one reason: a single clock removes the sentence "whose 8 o'clock did you mean".
Converting is addition, not magic. You add your UTC offset to the Zulu time to get local, and subtract it to go the other way. The part worth getting right is that the offset moves with daylight saving in most of the world while Zulu never does, so the same local time maps to two different Zulu times across the year.
Zulu time plus your UTC offset is local time. Below are the common Zulu times against a spread of fixed offsets — read down your column. Where the sum passes midnight the date moves with it, which is the part that turns a briefing into an argument.
| Zulu | UTC−8 · PST | UTC−5 · EST | UTC±0 · GMT | UTC+1 · CET | UTC+5:30 · IST | UTC+9 · JST |
|---|---|---|---|---|---|---|
| 0000Z | 16:00 −1 day | 19:00 −1 day | 00:00 | 01:00 | 05:30 | 09:00 |
| 0500Z | 21:00 −1 day | 00:00 | 05:00 | 06:00 | 10:30 | 14:00 |
| 0800Z | 00:00 | 03:00 | 08:00 | 09:00 | 13:30 | 17:00 |
| 1200Z | 04:00 | 07:00 | 12:00 | 13:00 | 17:30 | 21:00 |
| 1500Z | 07:00 | 10:00 | 15:00 | 16:00 | 20:30 | 00:00 +1 day |
| 1800Z | 10:00 | 13:00 | 18:00 | 19:00 | 23:30 | 03:00 +1 day |
| 2359Z | 15:59 | 18:59 | 23:59 | 00:59 +1 day | 05:29 +1 day | 08:59 +1 day |
These are standard-time offsets. Most of the columns move an hour under daylight saving — the Zulu column never does, which is the whole reason it is the one written down. The converter above uses your device's real offset, DST included.
Four digits and a letter. The digits are a 24-hour clock time exactly as in military time, and the letter says which clock they are on. Spoken, 0800Z is “zero eight hundred Zulu”; 1730Z is “seventeen thirty Zulu”.
Both 0800Z and 08:00Z are accepted in the converter above, and so is the colon form with a single-digit hour. Typing one of them gives the same instant back as local time, 12-hour, military, ISO 8601 and a Unix timestamp at once.
Three names, one clock, for every practical purpose. UTC is the standard — Coordinated Universal Time, kept by atomic clocks and nudged by leap seconds to stay within 0.9 seconds of the Earth's rotation. Zulu is how UTC is written and spoken in operations: the suffix Z, from the phonetic letter for the zero-offset zone. GMT is the older name, a time zone based on mean solar time at the Greenwich meridian, and it survives mostly in civil use and in the UK's winter clock.
The differences only matter to timekeepers. If a flight plan says 0800Z, a log says 08:00 UTC and a broadcast schedule says 08:00 GMT, they mean the same moment. What none of them mean is 8 o'clock where you are, unless your offset happens to be zero.
An airliner can cross four time zones between pushback and landing, and the crew, two control centres and a dispatcher may all be in different ones. Log the departure in local time and every reader has to know which local you meant. Log it as 0800Z and there is nothing to resolve: flight plans, METARs, TAFs, NOTAMs and ATC clearances are all in Zulu for that reason, and a pilot's logbook keeps block times on the same clock.
The same logic runs through military orders, satellite passes, incident timelines and distributed systems — a server timestamp is UTC for exactly the reason a NOTAM is Zulu. Daylight saving is the other half of it: a handover written in local time is ambiguous twice a year, once for an hour that happens twice and once for an hour that never happens. Zulu has neither.
The habit worth building is doing the arithmetic in Zulu and converting once, at the end, for the humans who need a local time. Add en-route time to a departure slot in Zulu, subtract the report time from the on-blocks in Zulu, then convert. Converting first and adding afterwards is where the day boundary gets lost.
Type the Zulu time; the converter shows the same instant on your clock, plus every other format.
The colon form works too — both 1400Z and 14:00Z are read as UTC.
Add en-route time to a departure slot; the result stays the same instant in every format.
Leave the box empty and it tracks the current time — the Zulu row is the current UTC time, live.
Zulu time is Coordinated Universal Time (UTC), written with a Z suffix such as 0800Z and spoken "zero eight hundred Zulu". Z is the NATO phonetic letter for the zero-offset zone, so Zulu time and UTC are the same clock with different notation.
Add your UTC offset. At UTC+2, 0800Z is 10:00 local; at UTC−5 it is 03:00 local the same day. If the sum passes 24 or drops below 0, the local date shifts by a day. Typing 0800Z into the converter above does this for your own timezone, daylight saving included.
For everyday use, yes — GMT and Zulu both mean the zero-offset clock, and 0800Z is 08:00 GMT. Strictly, UTC is the atomic time standard and GMT is a time zone based on the mean solar time at Greenwich; they never differ by more than 0.9 seconds, which matters to timekeepers and nobody else.
Never. UTC has no daylight saving, which is exactly why operations run on it. Your offset to Zulu is what changes: a place at UTC+1 in winter is at UTC+2 in summer, so the same local time is a different Zulu time in July than in January.
Four digits and a Z, no colon: 0800Z, 1730Z, 2359Z. It is spoken digit-pair by digit-pair with the suffix — "zero eight hundred Zulu", "seventeen thirty Zulu". Aviation writes the date with it as DDHHMMZ, so 141730Z is 17:30 UTC on the 14th.
Noon UTC, shifted by your offset: 07:00 in New York on EST, 13:00 in Berlin on CET, 21:00 in Tokyo. The converter on this page answers it for the timezone your device is in rather than making you count.