Realistic time allowance for domestic to international flight connections

Does anyone have a psychological comfort zone or sweet spot in terms
of time between connections that they look for if they have a US
domestic transfer on the way to Europe?

There is no magic answer, IMHO. For me, I look at every flight option in light of: departure and transfer airport busy-ness, time of year, time of day, checked bag/or not, airline, historic timeliness of flights in question, whether there are other flights on the same day if you miss your connection, personal experience with specific airports (looking at you, Atlanta), and relative cost of other more direct options.

Based on my personal preference, I would not choose a flight with a short layover as you listed. But that's me. On my next trip I have a 4 hour layover at MSP - definitely not my favorite option, but the alternatives were not in my comfort zone.

I would not be comfortable with either. I'd much prefer a longer connection time because I'd rather have extra time and perhaps be bored, than be short on time and be stressed about making the connection.

Under an hour seems tight for a large airport, especially when boarding starts 30 minutes or more ahead, and doors close 10 or 20 minutes before departure. I have done it for domestic to domestic connections, but to catch an international flight, I like a couple hours. Almost unfortunately, from my regional airport, my connections range from 4-10 hours due to the way the schedule flights out (lots of early morning and evening flights, few during the day.

Depends on so many factors. For example, 48 minutes at SeaTac (my home airport) is probably do-able under the right conditions and when everything goes smoothly (inbound flight is not late, you have carry-on bags only, you walk briskly, no kids in tow, etc.). But the problem I see is: what's your Plan B? I assume your SEA-CPH flight is probably on SAS (and BTW it's a lovely flight!) but they only go once a day (at best). If you mis-connect, when is your next option? Probably the next day (or later). For me, that's a deal-breaker on a tight connection.

No way I would take a 52 minute connection at LAX under any circumstances.

I do not mind burning a few hours (or even way more than a few hours) in airports. I'd much rather do that than fret, sweat, and get all stressed asking and worriying "are we gonna make it?" Been there, done that. Now I enjoy relaxing at airports. A few hours lost there is no biggie.

Surely anything under an hour must be asking for trouble I would think.

Yes.

I prefer 2 hours minimum, and I am OK with 3+ hours, very relaxing, eat a decent meal before boarding the international flight allows me to skip the airplane food, too....

Another factor is, what is the international airline you are connecting to?

If it's, for instance, United to United, then there is a good chance that the
international flight is departing from a domestic gate in SEA, and the connection
is almost as if it's a domestic connection. But if you have a connection to a
non-affiliated airline, and you have to change terminals, now the risk factor
does go up significantly. A Delta to Air France connection might be OK,
as they are both part of the same alliance. As noted, it pays to check on this
stuff ahead of time, preferably before you book a tight connection.

In Europe, this is not going to be as easy, as you have to clear passport control
on your first entry into Schengen, and also on the way out/home, so the risk factors
are higher.

Still, I have made a 30 minute connection (inbound was late) in Frankfurt, using
the e-gates.

As long as everything is on the same ticket, it's a legal connection, so at the least
the airline is obliged to get you there (eventually).

We have the same problem. Smaller CA airport that needs to connect to bigger airport then on to Europe. Last year we had a 2 hour connection at LAX; which would have been fine as it was Delta and Delta has it's own terminal so no changing from a domestic terminal to international terminal. They ended up changing the schedule and it gave us 4 hour layover which was going to seem long, but it was actually nice and no stress. We checked bags all the way through.

If you book all on one ticket it is their responsibility to get you to your final destination, but that doesn't mean it'll be convenient or on a timetable you like. I wouldn't risk such a short layover that you mention.

You could hop on Southwest or Alaska to SeaTac, or LAX and give yourself at least 6 hours. Keeping in mind it's separate flights; separate bookings; no transporting luggage from one to the other. Have to go through TSA twice if you have checked luggage you need to pick up and recheck, etc. Not saying this is ideal but it could be done.

It's all a gamble. Depends on how much of a risk taker you are.

I like to have 3+ hours. And I try and book the first flight out of the day - less chance of delay.

It depends on the airport, the time of year (weather related) and what type of aircraft your domestic flight is on. I dont know if this is just my perception, but I think the smaller regional jets get delayed more often than the lager aircraft, and sometime their gates are a lot further away from the international terminal. I used to fly monthly to Chicago on United or American on regional jets, and I think the flight were delayed landing 2/3 off the time. Usually waiting on the tarmac to unload,

Another factor to consider is that sometimes, the larger international flights start boarding one hour before departure. If your at the back of the domestic flight, it can take up some of that time just deplaning.

I think it all comes down to how much delay your first flight might incurred. The last time I came close to missing my international connecting flight was at AMS on my way home to the US. My Schengen flight was delayed by ~25 mins, which eat into my 1 hour 10 mins layover time. International flight to non-Schengen area means one has to go through passport control; so I ended up running in the terminal and barely made it to my international flight.

Since then I always make sure I have at least 2 - 3 hours layover time; the latter if it's a large and busy airport.

If I have a refundable free to change hotel reservation, don't absolutely have to be somewhere, and the airline that I bought the ticket directly with has at least two other flights leaving directly to my destination, I go for the shortest connection if the ticket price is significantly lower than the longer connections.

When we lived in Sacramento, we connected out of San Francisco, sometimes LA. You really need to give yourself two hours especially if you don’t fly United and need to go thru TSA again in San Francisco for their International terminal. And make sure it’s all on the same ticket.

Two to three hours for me but I rarely have connecting flights. I’m fortunate that San Francisco airport offers many nonstop options to get to major European cities. These days I structure my trip to get me to a gateway city like London, Amsterdam, Rome and either overnight or spend a few days there before moving on.

FYI. All the terminals at SFO are connected airside so a domestic to international connection may not require clearing security again. It would be.a rather long walk from the G gates to the A gates as you have to go through the other terminals.

https://www.flysfo.com/passengers/travel-tips/international-travel/connections