Southern line to Gatwick

Trains run every 15 minutes and take ca 35 mins; so in the unlikely event of there being no seats you wouldn’t have to wait long. My preference for departures from Gatwick would be to be there 3 hours before departure as it’s always been a crazy busy airport for departures to Europe. There are two terminals, the train stop is next to the South Terminal which handles most European flights; there is a shuttle to the North terminal - look for the signs as you head into the South Terminal.

A train can not be full, it can be standing room only, but not full as In not taking more passengers.

In the middle of the day, with the length and frequency of Southern trains it is vanishingly unlikely that there will not be seats available on any given service.

If you are going to Gatwick from Victoria, don't get the Gatwick Express - 3 minutes quicker but noticeably more expensive.

Two hours ahead is plenty- particularly if you have already checked in and are only travelling with hand luggage, so can go straight to security. Even if you have to drop bags, if you are flying on easyJet this is a very quick process at one of their many baggage drop machines where you scan the bags and put the tags on yourself. You can use contactless to Gatwick (unless you have a rail card and you want to get the discount, in which case you need to purchase a ticket online or at a machine). You can always get on these trains, even if they are full, which would be very unlikely this time of day as mentioned above.

A small correction above on the terminals. The vast majority of flights from Gatwick are within Europe, across both terminals. The main difference is that the North Terminal is where all the easyJet flights depart from, and they are indeed most of the flights at that terminal. Always check your boarding pass but in general, if it's easyJet it's North and if it's not easyJet it's likely to be South. Good luck and safe travels!

Thank you so much everyone! Great to know that we can board a train even if there aren't any seats left. Also great to know that it's unlikely there won't be any seats left and, as I understand it the trains seem to run every 8-12 minutes or so. Also thanks for the advice about the Gatwick express. We will be checked in the day before providing nothing goes wrong when we try to do it online. But we will be checking bags so I'm thinking that would be less stressful to plan to arrive at Gatwick 3 hours in advance. At first I thought that our flight will be considered domestic but then I remembered that England is no longer part of the EU. So I have no idea if this flight would be considered domestic or international. In any case, it's on British Airways departing from the South terminal.
Again, I really appreciate all the help.

It never was a domestic flight, that would be within the UK.
The distinction is more between short haul like this and long haul , to go to the States for instance. Thus this is two hour check in.

But the prudent person allows a bit of buffer time, as anything can happen on the way, whether travelling by road, train or private helicopter!!
So am!ing to be there around 3 hours before is never a bad idea.

Murphy's law of travel says a problem always happens when you least need it to, and. I guess there aren't that many London to Bordeaux flights a day.

On Southern the train will always be travelling to somewhere beyond Gatwick (a range of places) so on the departure screens it will be listed as one of the calling points, not the headline destination.