Datetime.Now or Datetime.Utcnow

Question

What’s the difference between DateTime.Now and DateTime.UtcNow ?

DateTime dateNow = DateTime.Now; // retorna {01/08/2018 18:28:15}
DateTime dateUtfNow = DateTime.UtcNow; // retorna {01/08/2018 21:28:15}

The clock on my computer is like: 18:28 and date 01/08/2018.

The difference I saw was 3 o'clock the most. When should I use Now and UtcNow.

Answer 1

The DateTime.Now returns the time set on the server and the DateTime.UtcNow returns the time in UTC which is the "Coordinated Universal Time", in case we have 3 hours difference precisely because you are running on your machine that is in Brazil and most Brazilian states have as time zone "-3 o'clock", on the map on the Wikpedia link you can see the states of Brazil with different hours:

• https://en.wikipedia.org/wiki/Time_in_Brazil

If you set up your computer to use the Acre state time zone you would probably see a difference of -5 hours from the DateTime.UtcNow.

Already using the method:

Console.WriteLine( DateTimeOffset.Now.ToUnixTimeMilliseconds() );

Or:

Console.WriteLine( DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() );

You will get equal results, because the method ToUnixTimeMilliseconds works with UTC as well, ie the Unix Epoch is based on UTC so the class internally probably compensates for the "time zone"

---

Imagine you have two individuals:

• Paulo in Acre (-5 hours in relation to UTC)
• Sofia in São Paulo (-3 hours in relation to UTC)

Paul sends a message to Sophia 18:01 (time in Acre):

I finished the prototype of the app, follow the link to test - ^{Time: 18:01}

Sofia will see it in almost the same moment it was sent, but for her it will be 20:01 and will respond back 30 minutes later:

Thanks Paul, I tested the app, it seems that this within the agreed, I await the publication in the store - ^{Time: 20:31}

João will receive the message at the same time, but he will view the message as his local time 18:31:

Thanks Paul, I tested the app, it seems that this within the agreed, I await the publication in the store - ^{Time: 18:31}

That is, if saving in the "bank" the time with the Timezone of the person would probably give problems, now if using in its hypothetical bank UTC without applying the Timezone, whether with Unix-time or by the bank itself ai it is sufficient at the time of reading the application to identify the user’s Timezone that is reading the message and adjust the value entered in the bank for its region.