GMT is the same clock as Zulu, and BST is 1 hour ahead of Zulu. Live clocks, the full hour chart and the daylight saving rule that catches people out.
Zulu time is UTC - the clock every flight plan, order and server log is written in, precisely because it never moves. Greenwich Mean Time (GMT) sits UTC±0, which makes it the same clock as Zulu. The two read the same, so there is nothing to add - the only thing left to get right is which clock the other side actually meant.
The converter above tracks the current time until you type into it. Enter any Zulu time - 1730Z, 17:30Z or NOW - and it renders the same instant in GMT in 24-hour, 12-hour and dated form. The chart below is the same conversion for every hour of the day, so it can be read without typing anything at all.
Every hour from 0000Z to 2300Z. Two columns, because the zone has two offsets: read the GMT column in winter and the BST column from the last Sunday in March to the last Sunday in October. A single column here would be wrong for most of the year. Where the sum crosses midnight the date moves with it, marked in the cell.
| Zulu | GMTUTC±0 | BSTUTC+1 |
|---|---|---|
| 0000Z | 00:00 | 01:00 |
| 0100Z | 01:00 | 02:00 |
| 0200Z | 02:00 | 03:00 |
| 0300Z | 03:00 | 04:00 |
| 0400Z | 04:00 | 05:00 |
| 0500Z | 05:00 | 06:00 |
| 0600Z | 06:00 | 07:00 |
| 0700Z | 07:00 | 08:00 |
| 0800Z | 08:00 | 09:00 |
| 0900Z | 09:00 | 10:00 |
| 1000Z | 10:00 | 11:00 |
| 1100Z | 11:00 | 12:00 |
| 1200Z | 12:00 | 13:00 |
| 1300Z | 13:00 | 14:00 |
| 1400Z | 14:00 | 15:00 |
| 1500Z | 15:00 | 16:00 |
| 1600Z | 16:00 | 17:00 |
| 1700Z | 17:00 | 18:00 |
| 1800Z | 18:00 | 19:00 |
| 1900Z | 19:00 | 20:00 |
| 2000Z | 20:00 | 21:00 |
| 2100Z | 21:00 | 22:00 |
| 2200Z | 22:00 | 23:00 |
| 2300Z | 23:00 | 00:00 +1 day |
The conversions people reach this page for, answered in one line each. The first time is GMT; the BST time next to it applies from the last Sunday in March to the last Sunday in October.
There is no arithmetic. Zulu and GMT are the same clock reading, so 1730Z is 17:30 GMT; only the notation changes.
Between the last Sunday in March to the last Sunday in October the zone is on British Summer Time, so the correction becomes add 1 hour instead. Same instant, different local label - 1730Z is 18:30 BST.
Controllers and forecasters often drop the minutes and write a bare hour: 16Z means 1600Z, 6Z means 0600Z. Pad it back to four digits and the chart above answers it directly.
Do the arithmetic in Zulu and convert once, at the end, for whoever needs a local time. Adding en-route time to a departure slot in local time and converting afterwards is how the day boundary gets lost. The Zulu time converter does both halves in one box.
The reverse direction is the same non-conversion: keep the time, add the Z suffix. 08:00 GMT is 0800Z.
When the clock on the wall reads BST, the correction is subtract 1 hour instead: 13:00 BST is also 1200Z. Same instant, one hour less to undo.
GMT itself is a zero offset and never moves - Zulu and GMT are the same clock reading. What moves is the UK: from late March to late October Britain runs on BST, one hour ahead of Zulu. So "GMT" on a British summer calendar invite usually means BST.
Zulu itself never shifts, so every hour of the shift lands on the local side of the conversion: UTC±0 in winter, UTC+1 from the last Sunday in March to the last Sunday in October. If a message does not say which, use the date it was written on to decide, and read the matching column above.
The Greenwich meridian is the origin of the whole system. GMT survives in UK civil time, in shipping and broadcast schedules, and as the everyday name people use when they mean UTC.
Flight plans, METARs, TAFs, NOTAMs and ATC clearances are all in Zulu, and so are military orders, satellite passes and incident timelines. The conversion to GMT is the last step, for the people who have to be somewhere at a local hour - a briefing time, a crew report, a maintenance window. Written the aviation way it carries the day of the month too: 141730Z is the 17:30 Zulu of the 14th, which removes the last ambiguity a date shift can create. See military time for the four-digit notation itself.
The same Z closes every ISO 8601 timestamp: a log line stamped 2026-08-20T16:37:05Z happened at 1637Z, and it converts to GMT with the same arithmetic as any briefing time.
GMT is the same clock as Zulu (UTC±0). 1200Z is 12:00 GMT - the two clocks read the same.
The abbreviation GMT always means UTC±0, but the clock it describes switches to BST (UTC+1) from the last Sunday in March to the last Sunday in October. Zulu never changes, so the gap between them is an hour smaller during BST.
0000Z is 00:00 GMT. On daylight time it is 01:00 BST.
Yes, for every practical purpose. Zulu is how UTC is written and spoken in aviation and military use - the Z suffix is the phonetic letter for the zero-offset zone. GMT is the older name for the same clock reading, though the UK itself moves to BST in summer.
The two are the same clock, so the time is unchanged - only the suffix differs, e.g. 08:00 becomes 0800Z.
Printed from tcalc.it - free Zulu time converters, hour charts and the daylight saving rules.