Do I have to clear immigration in both airports or just one?

You are a brave soul to attempt transiting through CDG on separate tickets. At CDG, you will clear inbound immigration, check in for your transatlantic flight, then outbound immigration, then security.

There is no way to know how much time to allow, but any one of the steps could take 30+ minutes. You need no less than 3 to 4 hours, longer if you are checking luggage.

It sounds awful indeed. Glad I asked before I booked :) For just the outbound international flight from CDG, how much time do you need to allow before departure to jump through all the hoops?

You don't go through immigration leaving the UK.

If you aren't a British subject then you will clear immigration leaving England. At CDG you clear inbound immigration, stay in the transit (airside) area, check in for your transatlantic flight then outbound immigration, then security.

In this scenario the common wisdom says you should be at LHR 3 hrs before that flight departs and should give yourself not less than 3 hrs at CDG. Add in the hour flight to CDG and by the time you board the flight to the US you will have been up at least 9 hrs. Hopefully you can sleep on the plane for a good part of a 9hr+ flight

Presumably you are doing this to save money? Sure hope it's big number

You need to be at CDG 3 hours before the flight but that is too tight on separate tickets because it doesn't factor in delays that are fairly common when flying. I would not do this with less than 6 hours. Stuff happens. I have had had atlantic flights come in 5 hours late. I have had the Thalys come in 5 hours late from Amsterdam to Paris.. Stuff happens. And missing a high stakes flight to the US is a big miss. And if you flat out miss it that ticket is gone.

The answer is "It depends".

If it's one airline and the same termninal at CDG: no, just passport control in London and the US.

If it's two different airlines and the same terminal for both flights at CGS: probably no, but possibly immigration at CDG.

Any other scenario, probably yes.

Your problem isn't really immigration, it's security. As long as you can stay airside of security at CDG you should be ok with 2 hours.

If you are on two tickets you cannot stay 'airside' in the transfer but will have to pick up luggage and check in for the second flight. You are flying to Paris from London and go through all the normal immigration and customs processes, then you check in anew for the separate flight which is why you have to be in the check out line 3 hours ahead. I don't believe you can do a correspondence when not on a single ticket. Or at least I would want authoritative information from the airlines that this is possible.

Janet

I have done it at airports other than CDG (I've never transferred through CDG). It depends on the airline you are transferring to having a desk airside in the terminal you're in that can do seat allocations.

This is a bit risky as delays can have huge consequenses. If it was my trip I'd take the train to Paris the day before. There are worse places than Paris to spend a night.

I am planning to spend time in Paris on the front half of the trip, and was looking for the most efficient way to maximize my time in London on the back half. However, with my outbound flight leaving at 11:15 am and processing times being what they are, it's clear I will need to be back in Paris the day before my flight to be able to make it on time.

Follow up question:

If I'm staying in the 7th arr, what would be the best time to leave for CDG to make an 11:15 flight on a Tuesday?

If I'm staying in the 7th arr, what would be the best time to leave for CDG to make an 11:15 flight on a Tuesday?

I would arrange for transportation pickup no later than 07h15.

I'm assuming you looked a multi-city flights into Paris and out of London, and found them too expensive?

I can understand the feeling that you want to spend as much time as possible in London. But in my opinion, going back to Paris for the last night is a better use of the time. You would need a bit of buffer time and if it my choice I'd rather spend that time in Paris than at Charles de Gaulle. And if your flight leaves 11.15, there is no way I would be comfortable spending the last night in London.

Any reason for staying in the 7th? The Eurostar arrives at Gare du Nord and the RER to the airport leaves from Gare du Nord, so why not stay somewhere in the 10th?

I enjoy staying in the 7th. I generally arrange for a taxi to the airport 4 hours ahead of departure as Tocard indicates. 1 hour to get to the airport and 3 hours to make my way thru the various lines.

I'm glad you have decided to go back to Paris the night before your flight. This is a much less risk-averse strategy.

The 7th is not set in stone, also looking at the 10th, 2nd and 8th. Location recommendations welcome :)

I am planning to spend time in Paris on the front half of the trip, and was looking for the most efficient way to maximize my time in London on the back half. However, with my outbound flight leaving at 11:15 am and processing times being what they are, it's clear I will need to be back in Paris the day before my flight to be able to make it on time.

I suspect I must be missing something, but would it not make more sense to do London on the front end and Paris at the back end of the trip, if Paris is where you fly from to go home?

or maybe instead of fly, take the Eurostar?

My inbound flight gets in at 9:30 am local time. Going through immigration, making my way from CDG to Gare du Nord, sitting on a train for 2 1/2 hrs then finding my way to where I'm staying in London sounds absolutely awful on top of a transatlantic flight, which is why I'm not doing London first. :)

We are planning to take the Eurostar to London, but I was hoping to expedite the return process by flying into the same airport I would be flying out of. Sadly, that is not a doable option given the time commitment involved.