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5 Answers

Tricks for converting UTC time to local time

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General Aviation

Would anyone like to share their trick for converting UTC time to local time.  I am constantly performing mental gymnastics to go from a UTC time to local.

 

So far the easiest way that I have found to make it easier for me is to remember what the local time is when it is 1200z and 0000z and then go from there.

 

I am interested in hearing if anyone has found a much simpler method.

 

thanks

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5 Answers



  1. Russ Roslewski on Dec 04, 2014

    The conversion from UTC to local time kind of has two components (for U.S. residents anyway), one which is simply subtracting the offset for your area, the other is converting from 24-hour time to 12-hour time that is commonly used in the U.S. but certainly not worldwide.

    So, for me in the Central U.S., at this time of year I need to subtract 6 hours. If UTC is 2251, I subtract 6 hours which is 1651 (22-6=16) in 24-hour time. Now, for people that didn’t grow up with a military or nautical background, that 1651 doesn’t mean much until you convert it to 12-hour time by subtracting 12 from the hours (if it’s 1300 or greater) and making it a PM time.

    So, 1651 – 12(00) = 4:51 PM.

    If it helps, mentally put a colon between the UTC time to split it up.

    So, 1732Z = 17:32, minus 6 hours = 11:32 (AM)
    2317Z = 23:17, minus 6 hours = 17:17, subtract 12 for “12-hr” time = 5:17 PM.

    Did I understand your question, and does that help a little?

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  2. Brent on Dec 04, 2014

    Every timezone has an offset from UTC. For example, it’s currently standard time here in Atlanta, so it’s GMT-05:00. The “trick” then is to just subtract 5 from the UTC time.

    Since I can’t imagine anything simpler than this, perhaps you’re really struggling with converting the 24 hour time to more familiar (in the U.S. anyway) 12 hour time? We’re just subtracting again, but you might find it easier to subtract 2 then subtract 10. So 1900 becomes 1700; drop then one and you have 7pm. You could even save a step and combine the 2 hours with your GMT offset. For example 2300Z works like (23 – (2 + 5) = 16; 16 – 10 = 6pm.

    Or perhaps the stumbling block is going across the midnight line? You might find it easiest to figure out the difference between your GMT offset and 0000, and then just count that back from midnight. For example, to get from 0500Z to Pacific standard time (GMT-08:00), you notice that 8-5 = 3, and three hours before midnight is 21:00 or 9 pm, if you prefer.

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  3. Mark Kolber on Dec 05, 2014

    I’m having difficulty picturing a simpler mental “rule of thumb” than knowing your local offset and subtracting or adding it to the UTC time (and vice versa), as described by Brent. For the 24-hour to 12-hour “translation” it’s really just subtracting 12 if the result is over 12. With times that end up negative after applying the offset, add 2400 – you do something very similar when you do a heading calculation that gives a result over 360.

    2200 UTC – 0500 (EST offset) = 1700 local time – 12 = 5 PM local time.
    0200 UTC – 0500 (EST offset) = -300 local time + 2400 = 2100 – 12 = 9 PM local time

    Personally I’m horrible at even that mental math and avoid it with a dual time setting on my watch and an app or chart on my smartphone and tablet.

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  4. tommytom on Dec 05, 2014

    I agree with you Mark! I’m not the quickest when it comes to the math. That is why I asked. Also wanted to share any tips or tricks with my students as well. The easiest way that I have found so far that helps me is just remembering what The local times are at 00, 06, 12, 18, 24…

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  5. Caroll on Jan 11, 2022

    > The “trick” then is to just subtract 5 from the UTC time.

    You are forgetting about added/subtracting additional time for Daylight Savings Time.
    In some states it\\\’s 0-1 hours more/less. Other parts of the world are 15 mins, or 30 mins, or 1 hour, etc.

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