TGV tickets at CDG reserve or not

If you can get them very cheaply 4 or 5 months out I'd get something 3 hours after arrival and hope for the best and just plan to buy new ticket if you guessed wrong. If you don't save much because your trip is very soon then no point doing that.

It took us 2 hours to get through immigration last April and 45 minutes this October but our plane was 2 hours late -- stuff happens, but most of the time if you have 3 hours you are good. Any onward trip the same day carries some risk.

TGV Inoui tickets (not Ouigo) can be changed up to departure time for a 19€ penalty plus fare difference. So, you are only risking 19€, and advance booking discounts are typically greater than that, so it is a risk worth taking. If your flight is super late, you can reschedule before you leave, and if you get delayed at immigration or luggage claim, you can use the app on the go.

This was last minute decision, we leave early March, no real savings pre booking. But was wondering if I could just wing it or if tickets are usually sold out the day of.

Also what's the best site to purchase them?

Buy on the Railroad of France official website
https://www.sncf-connect.com/en

Ticket availability depends on your final destination. You

Trains almost never sell out except on holidays and special days (possibly when rail service is limited for some other reason?) and you will be able to get a ticket on a train, though it may not be the "class" you want. I (along with many people) don't want to spend our arrival morning watching the clock trying to rush to catch a prepurchased train or watching the clock waiting around for a train we have purchased WAY later. I would just wait until you arrive and you will end up buying the most time convenient for you to arrive and get your bearings.

Trains almost never sell out except on holidays and special days

That's less and less true in France, demand is high. For example, both the 4.19 pm and the 6.19 pm from CDG to Bordeaux are fully booked tomorrow, and tomorrow is not a special day.

sorry, I was more saying "trainS"......like ALL the options you could have upon arriving into Paris be sold out and you would be scrambling to find accommodation when you weren't expecting. Does that happen normally? I am glad I am arriving into my first "destination" and I just have to hop on a tram and purchasing my long distance tickets WAY in advance.

I agree with Balso, more and more are selling out. Someone could end up waiting a long time for an available train if several are sold out. The example Balso gave for tomorrow would mean someone has to wait several hours.
Last summer during the heat wave once trains in the southwest were rolling again, they were full. My husband had to drive to Paris with friends and take a train home via the Rhône Valley because everything was sold out on the Bordeaux -Marseille route. So it happens.

huh, learn something new every day!

But if one were to book a ticket with a generous enough time frame (or even with a tight one that you would be missing and needed to change) to catch from the airport to save stress but wanted to switch to an earlier one (or later if you picked a too early one) for the 19 euro change fee and then the train was sold out, you would still be waiting until another train was available.......so there is always a chance of a long wait!

But now my brain is coming up with all different scenarios....I guess I would need to research, but to get into Paris from CDG you wouldn't have a train to book, since it would be an RER, right? Wouldn't getting into Paris proper turn up way more train options than looking for a train direct from CDG? Would you really be stranded in Paris for a night because you didn't purchase a train ticket in advance?

Just talking through options, not trying to be difficult haha :)

Yes, you take the RER into Paris. Yes, there would be more options from Paris. It's unlikely you'd be stranded in Paris during normal times...

but I almost was recently, December 23rd, when our tour agency in Paris made an error. I looked at options in case I had to return home to the south of France. There was neither a train nor plane seat to my city for a couple of days.
So yes, trains could be sold out for those traveling around big, big holidays.

Now you are thinking like us...looking at options and not counting on everything running like clockwork. As I'm writing this, I'm waiting to see if my two trains Saturday will be cancelled due to the controllers' strike. Update: One of my trains is cancelled. Decision time. Flixbus, BlablaCar? Postpone? C'est la vie in France.

PS When we take the TGV to the south after a transatlantic flight, we book 3-4 hours after arrival. I'd rather wait in one of the boulangerie cafés or have breakfast at the Sheraton than run for a train.

parikahs,
Last year when booking tickets for our daughter and her kids to get to Bordeaux from CDG after a flight from the US, the TGV train departure times to Bordeaux were either too close for comfort after arrival (about one hour), or entailed a 6+ hour wait and a late-ish arrival in Bordeaux. They were to be driven to the Dordogne area that day (about a 3 hour drive), so not a great choice. I opted to get the flight tickets from the US to Bordeaux, with a plane change at CDG. Although she had just under two hours for the plane change (and terminal change), she made it in good time and arrived in Bordeaux at a good hour for the drive to La Roque Gageac. The second flight was on the same ticket as the first, so it was a comfortable decision for me. The price difference was not great either. Just a possibility for you to consider.

parikahs,
I want to add that she was traveling with a 9 year old and a 12 year old, so ease of transfer was uppermost in my mind. The first flight was 10-11 hours, so everyone was a bit tired, and they were unfamiliar with CDG. (We did get premium economy, so that helped.)

Trains do sell out. We could not get tickets on reserve seat trains from Carcassonne to Montpellier last minute last fall and had to scramble to get seats on a very crowded TER later than we wanted. I am pretty good at snagging seats in a crowd, but it was touch and go -- and we are very old and not really up for standing for a train trip even one that was only a couple hours.