Gatwick / transportation

Is your outbound flight from Gatwick back to the US, or are you going elsewhere in the EU after London?

I took that route last Oct...lucky that it exists which I only found out during my 11 night stay. The Thameslink is direct Gatwick to St Pancras Station, takes one hour. Since I stay in a B&B in KingsCross/St Pancras, that train is ideal. Cheap too, with the Oyster card the fare two GBP less than the normal fare.

I'll be going back at the end of April, landing at Gatwick at 0950. Clearing Border Control quickly is chancy I allow myself 15 mins to more than one hour. What can be counted on is that once I board the Thamelink, I can expect to be at St Pancras in one hour's time.

I think you should take a Southern train to Victoria (cheaper than the Gatwick Express, just buy tickets on the day) then take the Circle Line round to Bayswater.

On the Sunday you would likely return, once again, from Victoria to Gatwick.

I had been musing whether to suggest changing at Clapham Junction, taking the Overground to West Brompton and the District from there, but I think it is pretty much a wash for time.

What time is your flight home? Traditionally there are fewer trains on Sundays and they start later in the day. Sundays often see planned engineering works on the Tube and railways; with more specifics a more specific answer can be provided.

Conventional wisdom on most carriers from most airports is to allow a minimum of three hours before departure to the USA at the airport.