Subnetting Made Easy – Formula

I covered subnetting in my earlier posts, Subnetting Made Easy, Part 1 and Subnetting Made Easy, Part 2.

In the latter mentioned post, I explained how you can use simple additions or subtractions to work out the First Usable Address, the Last Usable Address and the Broadcast Address of a subnet.

As the post was quite long, I thought I should re post the formulas in case they got lost in the sea of text.

Here they are:

  • First Address = Network Address + 1
  • Broadcast Address = Next Network Address – 1
  • Last Address = Broadcast Address – 1

If they make no sense to you, please re-read my previous posts for more information.

Other Posts in this Series:

See the Subnetting Made Easy – Index post for links to all of the posts in this series.

As always, if you have any questions or have a topic that you would like me to discuss, please feel free to post a comment at the bottom of this blog entry, e-mail at, or drop me a message on Twitter (@OzNetNerd).

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