Adequate layover time to get thru customs

If your US to Rome is a single booking, the airline will build the into the connection time the time needed to clear passport control .

Same for the return trip.

If you are cobbling together multiple individual flights, the common advice is not less than 3 hrs.

And you will soon be getting a lesson on 'customs' v 'immigration' (i.e passport control)

Good points! It's been a few years since we've flown to Europe. We're flying from Salt Lake City, so we'll likely fly on Delta all the way through. They typically fly through Atlanta, JFK, Chicago, Paris, and Amsterdam.

As others have noted, many variables, and need more info, but here's somethings to think about...

The listed minimum connection time in AMS for a non-Schengen to Schengen, Delta to KLM flight is 60 minutes (see info here). Coming back, the MCT at JFK depends on which airline(s) you're flying, but let's say 1:45 (see info here).

Since you're talking about connecting in AMS and JFK, I imagine you are looking at flying Delta/SkyTeam. Do you have any status with them? Gold/Elite Plus will allow you to use the priority lanes for immigration in AMS. Travelling in business/premium economy will also allow this.

Do you have Global Entry? This can make a huge difference at JFK (doesn't help you at AMS.)

It also depends on some other factors--how many other international flights are arriving around the same time, where you are sitting on the plane, and, the biggie, is your flight on time.

Having said all that, it also depends where you fall on the risk-averse scale. Would you rather reduce the risk of missing your connection or spend as little time as possible in the airport? As someone else once posted about connection times--you can be stressed or bored, the choice is yours. Personally, I generally do at least 2 hours if the itinerary is one ticket.

Assuming you mean connection time, not layover (Google the difference), it matters which airport it is. Some, like LHR or CDG need a lot more time than others, like Schiphol. If you aren't wanting a layover, but just want a fairly quick and efficient connection, just enter your departure and arrival airports into the air website's search boxes. That will bring up your flight and connecting city options. Minimum connection times are built into the search algorithms. But if you have mobility or other concerns (directionally challenged?) then select flights with a longer connection time.

On the flight over, you won't go through Customs at your connecting airport; just Immigration. But on your return flight you will have to go through both, and if it's JFK, I'd want AT LEAST 2 hours.

I've flown Delta and its partners on 25 trips to Europe since 2014. Delta is pretty reliable, but things happen. If I am connecting from a US airport to my final destination in Europe, I usually give myself a big buffer -- often something like 4 hours (usually enough time to catch another flight to the connecting US airport) so that I don't miss the one flight to the European destination for the day. If I'm connecting to my final European destination through Amsterdam or Paris, I like a minimum of 90 minutes.

For return trips, I like at least 90 minutes when connecting through Amsterdam or Paris. For JFK/ATL/DTW, I like a little longer, due to having encountered long immigration lines at all 3 airports if several international flights arrive at the same time; I like to have at least 2 hours for connecting in these US airports. I rarely check bags, but passengers with checked bags must pick up their bags before customs and drop them off after customs at JFK/ATL/DTW, which can further extend times.

The other thing I will mention is Delta's fall schedule right now is barely an educated guess. Throughout the pandemic, Delta has made major adjustments to its schedule around 6 weeks prior to the beginning of any given month (usually on the 3rd Saturday of the month that precedes the updated month by 2 months; e.g., significant changes were rolled out for the May schedule on March 20). There is a good chance anything scheduled now will be changed a time or two before you make the trip, which may mess with you best-laid connection time plans.

Delta has in the past had direct flights to/from Amsterdam , Paris and Heathrow from Salt Lake City - we've taken them. Not as many per day as Atlanta but they have had them. Just did a search on their site and they still have flights to Paris and Amsterdam.

Time to clear immigration depends on how many other international flights arrive at the same time. In both Amsterdam and Paris we've had short waits and long waits. Very hard to predict.

Re return you mention "layover" at JFK. Are you passing through (ie: connecting) or will you be staying in NYC for a spell?
If the latter then going through Customs is no biggie. If the former you will probably arrive at JFK during "prime time"; ie: lots of packed flights at the same time which means long lines and delays. Unless you have Global Entry be prepared for lots of waiting.
If you are flying Delta a better return would be flying into Detroit and then connecting back to your destination. Less traffic in Detroit - primarily Delta flights as it is one of their hubs.

Thanks for all this great info. I should have said "connection" instead of "layover". I like to err on the side of caution, so I guess I'd rather have a longer downtime in the connecting airport than a stressful run through the airport. I just hope Italy is open to tourists by then!

If you can possibly do the AMS -> SLC flight on the way back, do it! Pre-pandemic I flew yearly via SLC and really it's a pretty easy location for incoming Immigration and Customs. The longest wait is usually for baggage that you pick up after Immigration but before Customs, carry thru, then drop at the Delta desk for your onward flight right outside the Customs area exit. There are a few international flights to SLC, mostly from Mexico, but I've never encountered another incoming flight at the same time.

I'll add that the last time I flew home from Italy, transiting thru AMS I had to leave Milan at 0-dark-30 to get to AMS for the SLC bound plane. I swore I'd not do that again and would fly to AMS the afternoon before.

I like to have at least 2.5-3 hours at whichever airport I'm doing Immigration. I know many feel that is overkill. At least at AMS there are plenty of flights to Rome in case you miss yours, lol.

We have also done the Detroit/Amsterdam linkage. Remember the underwear bomber.

"Chicago and London don't work with Delta"

Pre-pandemic there was non-stop service from SLC to London Heathrow. I've taken it several times. Unknown, of course, what the schedule will look like when we are able to start traveling again.

Looking at the Delta site, I see a routing via LAX that may be worth considering. ("Lowest fare")

SLC-LAX-FCO ( 3hrs at LA)

The LAX-FCO flight is long enough that you have time to get some meaningful sleep. Stopping on the US east coast looks least appealing ( for me anyway)

For a bit more $$ the SLC-AMS-FCO, looks good.

In any event, booking the single ticket has the airline doing the work of figuring out how long the stop needs to be, to make the connecting flight.

Hope your plans work out, and the 14 day quarantine requirement has been lifted when you plan to go.

If your US to Rome is a single booking, the airline will build the
into the connection time the time needed to clear passport control

They actually will not. But they will rebook you when that 1 hour connection proves to be a pipe dream.

I appreciate everyone's insights. It might be a bit early to buy tix, considering the state of Europe right now, but I'm dying to start traveling again! And I'm wondering if flight prices might start climbing once Covid starts slowing down over there. Anyway, thanks, world travelers!

SLC-LAX-FCO ( 3hrs at LA)

I'm going to guess that second segment is Alitalia, and I would be very hesitant about booking it unless I was willing to lose that long non-stop and know I could very well be flying through different cities. Alitalia (or ITA, or whatever name they end up flying under) is still trying to figure out who's going to own them and if they will still be part of SkyTeam.

I have made connections in Europe (Frankfurt and Istanbul) in one hour. It can be done and is often done. But If you do miss that connection, while they will put you on the next flight, that next flight could be then next day. Not worth it on a vacation trip. My preference is 2.5 hours minimum and 3 hours at Heathrow and Chucky D.

If you make a connection where your checked luggage will be sent through, you still may face a lengthy security check for your carry-on bag before your second flight. Some major airports have centralized this process for all airlines, rather than leaving it to the individual carriers at their respective departure lounges. That central scrutiny, often right after passport control, can be crowded.

If the travel is on a single itinerary and misses the connection, the airline is responsible to put you on the next flight (that has room.) It could be a long wait, and certainly stressful. As a precaution, it's wise to have the airline schedule available, either printed out or stored electronically, to help negotiate for the replacement flight. I'd rather build an extra hour or two into the connection, knowing what to face, rather than worrying about the unknown.

"Right but Delta won’t codeshare with BA or any nonstop from London to Rome.'

Oh, I see what you were getting at in your other post. I didn't pick up on what you meant as to why London was in there and wanted to make sure others knew if London was in the mix then it's an easy non-stop service from SLC.

Wow, lots of new info to consider. Thank you!

Anyone citizen returning to the US without Global Entry should use "Mobile Passport" to breeze through customs. Sometimes it's even faster than GE!

https://www.cbp.gov/travel/us-citizens/mobile-passport-control

I try to fly into my final city directly if possible. That means
having my connection (layover) here in the US. Being in the west
myself I also try to make them in the mid-west to western US with
overnight flight so I can get some sleep. My next trip (hopefully)
will be ANC -LAX-HEL-CPH on one ticket. It gives me 1.5 hours in
Helsinki for passport control and being a small, efficient airport
that's more than enough time. If I was connecting in Paris or
Frankfurt I would look for 3 hours. May not need that much but better
safe than sorry.

If you try to fly into your final city, there are direct flights from Los Angeles to Copenhagen.

A small piece of advice regarding Helsinki airport, is might not be as small and efficient as you think. Sure, it is no Heathrow or Charles de Gaulle, but it has grown quite a lot in the last five years and there have been reports about long immigration lines as the airport was not designed to handle as many passengers. They are working on expanding the choke points, but they are not done yet. I wouldn't worry about 1:30, but be aware that it might not be as much time as you think.

I'm going to guess that second segment is Alitalia, and I would be
very hesitant about booking it unless I was willing to lose that long
non-stop and know I could very well be flying through different
cities.

I would hesitate about booking Alitalia as well given their current state. But, I would not be that hesitant booking it via e.g. Delta. If Alitalia goes under, you still have your Delta ticket and they will reroute you. You might not arrive at the same time you expected though.