Gare Du Nord To CDG

Buy it at the station from the machine.

10.30 EUR per person. Takes about 35 to 40 minutes, depending on what terminal. Trains about every 10 to 15 minutes. These are not SNCF trains, they are RER trains operated by Paris Transit Authority (RATP).

What Sam said. You do not want an SNCF train; you want the RER, which is run by the Paris transit company. Just buy the ticket from the machine when you arrive at the station if you don't have a Navigo Decouverte pass. You'll need to leave before 3:00- that's about the time you should be arriving at CDG for an international flight home. You'll probably want to catch a train leaving around 2:30.

To be exact, that one line, the RER B is owned by SNCF. However, you ignore that and use an RATP, or Paris transportation ticket. You don’t buy a ticket in advance from SNCF. That’s a detail that concerns only people working on that line, not us the passengers. As others have said, get your tix at a metro station, any metro station. Gare du Nord is a metro, an RER, and a train station. As CJean said, you need to leave around 2:30 if you are flying internationally outside Europe.

you can buy the ticket whenever convenient; I don't like to buy this sort of ticket last minute, but have it in hand ahead of time. One fewer thing to have to worry about doing before a flight.

Where is your flight to at 6:15 pm?

Based on an earlier thread, I suspect that the price and journey time the SNCF website is quoting you involves getting a TGV out to the first stop going north and then a different TGV back to CDG. Don't do this. Book a ticket on the RER as others have advised.

At Gare du Nord you can buy a ticket either from an automated machine or ticket window for the RER B to CDG. Follow the signs to the RER B. It's roughly ten euro (I've bought at least a handful of them, you'd think I'd recall the price?) and takes 45-50 minutes. After you get off the RER, there is an automated rail outside the station that takes you to the terminal you need.

Note the RER B line splits before CDG. Not every train goes to the airport. If you study the stops on the signage, you can tell whether a train will follow the CDG route or split off on the other route. A couple times I've gone out of Gare du Nord around rush hour and it's packed. In those cases, I catch the first RER; if it's not going to CDG, I get off before the split and wait at a less crowded station.

I've been pleased with the RER, it's reliable and inexpensive. I only have a small shoulder bag when I travel. If the train is crowded and you have a lot of bags, you should use extra caution to defend from thieves who ride the train and prey on tourists.