Dr. J's Maths.com
Where the techniques of Maths
are explained in simple terms.

Comparing times between places.


A frequent need is to determine what time it is somewhere else where a friend may live or be on holidays. To solve such a problem:

    1. find the UTC zone information in the two places;
    2. determine who is to receive the phone call or email, etc.
    3. subtract the receivers UTC zone rating from the other. If a positive result, the receiver is ahead. If a negative result, the receiver is behind.

 

Example 1:

I might be in Sydney, Australia in December (Eastern Summer time - UTC +11 hours) while my friend Evie is in Florida, USA (Eastern Standard Time - UTC -5 hours).

It is now 9:00 am Friday in Sydney. Should I ring Evie?

Evie is to receive my call - so start with her UTC zone and subtract mine. So -5 - 11 = -16. So Evie is 16 hours behind me. Her time is therefore 5:00 pm on Thursday. So no problem in ringing her.

 

Example 2:

Evie wants to call me because she wants to talk about a maths problem. It is 10:00 am on Saturday morning in Florida. Is that a good time for me to talk about maths?

I am in Sydney to receive Evie's call. So start with my UTC zone and subtract Evie's zone. So 11 - (-5) = +16. So I am 16 hours ahead of Evie. That makes it 10:00 am Saturday (Florida) PLUS 16 hours - so 2:00 am Sunday in Sydney. So yes a good time to call as it is always fun talking about Maths.

 

Example 3:

Evie is not sure of my number so she rings her sister Mimi in Paris at 9:30 am (Central European Time UTC+1 hour). What time does Mimi receive Evie's call?

Start with Mimi - so 1 - (-5) = +6. So Mimi is 6 hours ahead of Evie - therefore 4:00 pm on Saturday afternoon in Paris (c'est magnifique).

 

Now try some exercises yourself - in the web page Times in the UTC zones.