Transport from Heathrow to Gatwick

3-4 hours if not more. Heathrow can take a LONG time depending on just sheer luck on how long the customs lines are (had it take anywhere from 15 minutes to 90 minutes) and the bus takes an hour or so I've heard.

Is this on one ticket (e.g. both segments on BA) or are you buying a separate ticket. If it is on one ticket, BA defines a legal connection between LHR and LGW as 3 hours. Personally, I think that is extremely tight, but technically on one ticket they would be required to get you to your final destination if your first flight were delayed for any reason. I think 4 hours on a single ticket is better. If on a separate ticket, I'd allow more time.

Barbara - If you are travelling on separate tickets, allow more than 4 hours for the connection. In my only experience with a direct transfer from LHR - LGW it took over 4 hours just to get to Gatwick. I've never had a problem with Immigration at Heathrow, so I can't comment on that - the most I have spent in line over the past 10 years is 10-30 minutes. I guess I just have been lucky. As for the Gatwick connection, we didn't find that to be as easy as we though. By the time we got to the the right place, we had to buy tickets and they were sold out for the next several buses. We ended up waiting around 90 minutes and our bus never showed. I'm not sure if it was an exception but we finally got the people managing the passengers to let us onto another bus (our tickets had the bus numbers) and we finally were on our way. In all I think it took over 3 hours from getting off the plane and then finally on a bus to Gatwick. The bus with no traffic was about an hour - that was around 11am on a Sunday morning.

Thanks for your replies! I have decided on a different tactic to reach my final destination since I don't really want to spend so much time with all the transfers. I really appreciate your help. Happy Travels!