I'm trying to book a train journey in France for September. We are currently in May and the SNCF website does not allow me to reserve tickets such a long time (4 months) in advance.
So here is the question: how early can I reserve train tickets in France?
To complement other answers, indeed the sales start exactly 90 days in advance on most trains - TGV and Intercités as @audionuma quoted. Be careful though, some trains like regional ones have specific fare policies that include different starting dates, and that depends on each region (e.g. I tried on the PACA TER website and I could add a ticket to the cart for a trip in 1 year). The price and availability does not vary on these regional trains so no need to book in advance though.
However, some products sometimes have different policies on the starting date, in particular iDTGV, Ouigo, TGVs and Intercités.
For the TGVs and Intercités, there are three periods of the year when tickets may be sold earlier: Christmas, winter holidays (usually in February) and the summer. If you have a SNCF fidelity card or are a member of Capitaine Train, you shall receive emails warning you in advance of the sales opening for these popular periods.
Here I quote an email received on March 28th that sales for the summer (until August 30th, the last sunday of the summer holiday period) opened on April 2nd:
Pour vous remercier de votre fidélité, nous avons le plaisir de vous informer en avant-première de la prochaine ouverture des ventes de billets de train pour voyager cet été ! Tenez-vous prêt(e) ! Le 2 avril dès 6h, TGV et INTERCITÉS ouvrent les ventes pour vos voyages jusqu'au 30 août 2015 en France et quelques destinations en Europe !
I received similar emails for other periods, so in the end the advance booking was available as follows:
These are indicative dates, if you plan on travelling for popular periods and want to take advantage of low prices, you should expect to book around these dates in future years.
For Ouigo, a service intended for low-cost travel, and for iDTGV, another TGV service, the dates are different:
So in the end while the common rule is that sales are opened about 3 months in advance, this varies a lot depending on what train you want to take. If you want to travel during school holidays in particular, the sales opening may be earlier (or later) than the usual three months. If you want to be notified by email of these sales openings, you can signup for an account at voyages-sncf or Capitaine Train.
This page (in French) from SNCF http://aide.voyages-sncf.com/toute-laide-train/je-prepare-mon-voyage/informations-pratiques-horaires-trafic-gares/ouverture-des-ventes mentions that the opening of sale is usually three months in advance.
It basically says that the opening of sales for TGV and Intercités trains begins three months before the travel date.
On the same page, as of may 3rd 2015, it also mentions that sales are currently opened for travels from July 3rd to August 30th. (And not 31st, God knows why)
That is somehow contradictory with the first sentence. (As August 30th is more than three months away from current date). And I can confirm that searching for a ticket on August 30th is working on May 3rd.
Which means you have to keep an eye on the sales opening when looking for a distant travel date. The opening sales date seems to be between 4 and 3 months.
From experience I say 3 months, but not sure whether that is 90 days regardless of length of the months, or same day of the week or same date regardless of month. You will have to check out a few trains and keep an eye out just before the expected period.
The one exception I have seen on this rule is the Eurostar, which allows a 4 month early booking, making it harder to combine it with regular trains in France.
