Would it be terribly difficult and/or time consuming to transfer from a domestic flight into Gatwick to an International flight at Heathrow? How much time would I have to allow between arrival and departure?

Thanks!

Very easy - but long. There is a direct/frequent express coach that connects the two airports.

You'll want at least 4.5 hours between flights. More would be better. You need to clear immigration, collect your bags, get to the coach stop, and then clear security after you get to LHR.

What janisj really meant was that arriving on a domestic flight at Gatwick saves you little time in all this compared to arriving on an international flight.

You've still got to wait for your bags, get to the bus stop (National Express buses have an erratic timetable, averaging a departure every 15 mins, but there's sometimes as much as 30 mins, or as little as 5 mins, between buses), deal with the M25 (rarely as big a problem as its reputation, but there are often moments you think you'll never arrive), and go through security and baggage drop at LHR even if you've got a boarding pass already.

Getting a taxi saves almost none of this (it can't go any faster than the bus, though from Gatwick South or to T4 or T1/3 the bus spends an awful lot of time driving round airport terminals), you've got to pay for the connection and if your local airport has direct flights into LHR it's highly unlikely the net saving flying into LGW will be remotely worth the added hassle and uncertainty.

oops--missed the 'domestic' bit. sorry. But you'd still want a generous amount of time.

in my opinion this is something not only time consuming but implies lots of anxiety is it worth it?

If you have any other option then don't.

EVEN if you are on a single itinerary then you'll need to collect luggage, pay for the coach (£24.50) between airports or around £60 for a car service, check in again and go through the hassles of security - if you are flying BA from T5 then there are rules regarding the cut off time for passing through security and getting to the gate. You need to allow 5 hours between flights on a single itinerary.

If you are on separate tickets then allow a LOT MORE as there's nothing as embarrassing as missing your international flight and having to buy new tickets at full cost.

Consider flying via other hub airports - eg Amsterdam - so you don't have to change airports.

Thank you all for the feedback. I figured the transfer would be pretty painful but thought since I would already be in travel mode, I would just keep going as opposed to the alternative which would be to do a layover in London and leave the next day from Heathrow.