GMT time is Greenwich Mean time. It is also called UTC time or Universal Time, and zero meridian time. It is essentially at the zero hour. Every other time zone is given a designation of a set number of hours ahead or behind GMT (represented by a + or – next to a number) like GMT +1, or GMT -5.

For instance, eastern time is GMT -5, because it is 5 hours behind GMT time. When it is 12:00 noon GMT, it is 7 AM in Eastern Time Zone. Or, 12:00 – 5 hours which is 7:00 AM, or 700 military time.

Same for GMT + 1, Paris’ time zone. When it is 12:00 noon in GMT (or London) it is 1:00 PM in Paris.

If you imagine time zones on a scale from -12 to +12, each number designating a time zone, then GMT is at 0. GMT + 1 is at 1, GMT +2 is at 2, and the same in the other direction.

The other time zones are their corresponding number of hours behind or ahead of GMT time.

So, you can easily find the time in another city in another time zone using the numbers beside GMT.

Here’s how to find your own current time using GMT number codes:

  1. Find your time zone’s corresponding GMT Number (+1, +2, -5, etc.)
  2. Find the corresponding GMT time zone number
  3. Subtract your value from the other time zone value. Take the difference bewteen your corresponding GMT number and the other time zone’s GMT value, accounting for negative addition/subtraction rules.
  4. Add this value to your current time (or any other time you want to convert using GMT)
  5. The result is the time in the time zone

Here’s an example conversion you can do in your head:

It’s 8:00 AM in your time zone. You want to find the time in Paris.

Find your time zone GMT number which is GMT -5. Find the Paris GMT number, which is GMT +1.

Subtract your value from the Paris value or -5 from +1.

((-5) – 1) + 8:00 = 2:00 in Paris

Breakdown the formula:

((-5) – 1) = 6

6 + 8:00 = 2:00 PM

You can also convert this in military time. It is easier to do it this way. Just add the hours and do not convert to 12 hour format.

((-5) – 1) = 6

6 + 8:00 = 14:00 in Paris

Now, you’ll know what time to meet your girlfriend for coffee, when she suggests you meet at 14:00 in a coffee shop in Paris!