HST is 10 hours behind 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. Hawaii Standard Time (HST) sits UTC−10, which makes it 10 hours behind Zulu. In everyday speech the zone is just "Hawaii time". Converting one to the other is a single addition, and the only two things that go wrong are the date and daylight saving.
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 HST 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. One column is enough - HST keeps the same offset all year. Where the sum crosses midnight the date moves with it, marked in the cell.
| Zulu | HSTUTC−10 |
|---|---|
| 0000Z | 14:00 −1 day |
| 0100Z | 15:00 −1 day |
| 0200Z | 16:00 −1 day |
| 0300Z | 17:00 −1 day |
| 0400Z | 18:00 −1 day |
| 0500Z | 19:00 −1 day |
| 0600Z | 20:00 −1 day |
| 0700Z | 21:00 −1 day |
| 0800Z | 22:00 −1 day |
| 0900Z | 23:00 −1 day |
| 1000Z | 00:00 |
| 1100Z | 01:00 |
| 1200Z | 02:00 |
| 1300Z | 03:00 |
| 1400Z | 04:00 |
| 1500Z | 05:00 |
| 1600Z | 06:00 |
| 1700Z | 07:00 |
| 1800Z | 08:00 |
| 1900Z | 09:00 |
| 2000Z | 10:00 |
| 2100Z | 11:00 |
| 2200Z | 12:00 |
| 2300Z | 13:00 |
The conversions people reach this page for, answered in one line each. HST has one offset all year, so each answer is always right.
Take the four digits, subtract 10 hours, and roll the date if the result falls outside 00:00-23:59. 1730Z becomes 07:30 HST; 0200Z becomes 16:00 HST the previous day.
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.
Going the other way is the same arithmetic reversed: take the HST time, add 10 hours, and write the result as four digits with a Z suffix. 02:00 HST is 1200Z. If the sum crosses midnight the date moves too, exactly as in the chart, just in the other direction.
Hawaii opted out of daylight saving, so HST is UTC−10 all year - one column and no seasonal correction. It is also the furthest-behind US zone, so most Zulu times convert to the previous day in Honolulu.
Because neither clock shifts, a conversion written down today is still right in six months. That is unusual - most of the abbreviations on the sibling pages have a second offset for half the year.
The Hawaiian islands, including Pearl Harbor and Hickam - INDOPACOM headquarters. Pacific operations are planned in Zulu and lived in HST, ten hours apart.
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 HST 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 HST with the same arithmetic as any briefing time.
HST is 10 hours behind Zulu (UTC−10). To convert, take the Zulu time and subtract 10 hours: 1200Z is 02:00 HST.
No. HST stays on UTC−10 all year, so a single conversion works in every season. Zulu does not change either.
0000Z is 14:00 HST the previous day. The date rolls back, which is the shift people most often lose.
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.
Reverse the arithmetic: add 10 hours and add the Z suffix. Do the maths in Zulu first and convert once at the end - converting first and adding afterwards is where the date boundary gets lost.
Printed from tcalc.it - free Zulu time converters, hour charts and the daylight saving rules.