Your passport expiry is so important!!
As a blanket rule, you need 6 months validity left on your passport to travel internationally. What does this mean? Your passport needs to be valid for 6 months from the day you return home. So, while you have your passport out, check the expiry date. Do you need a new passport? Organise this before you book your flights.
For example: you are Australian and travelling to the UK for a holiday. You fly from Sydney to London on the 1st of May 2018 and then fly home from London to Sydney on the 29th of June 2018 and arrive in Sydney on the 1st of July 2018. Your passport must be valid until the 1st January 2019 (6 months from the day you arrive back home). There are lots of different situations where this is not the case (some countries only require 3 months validity), but as a general rule, use the 6 months as a guide.