As of Friday 5th August 2005, the UK were on Episode 3900, while Australia were on Episode 4020. This makes the UK 120 episodes behind, which is 24 weeks, or approximately 6 months.
Didn't they used to be much closer together?
Yes they did. However, when Home and Away moved from ITV to Channel 5, no episodes were shown for a whole year due to a clause in Home and Away's contract with ITV! So that's why we're so far behind now.