First time solo traveler 1 week in September

We had beautiful weather in Copenhagen and Oslo the first week of September 2023. We were in Copenhagen for 3 nights and Oslo for 3 nights and felt another night in each city would have been better to comprehensively see them. Keep in mind the first day or two after you arrive in Europe you’ll be jet-lagged and not moving at 100%. Just one week to include 3 capital cities plus one more city is not enough time. The high-speed trains from Copenhagen to Stockholm take 5 hours, and 4.5 hours from Stockholm to Oslo. These transfer times will each use up more than half of a day which is basically an entire day. for the two transfers. That leaves you with 6 days.

I've been in June and it was a fine time to go, though no way to predict weather for either month. But either way there is too much for seven days, even if you're used to going fast. I'd pick two of the four places you listed. Otherwise you'll be mostly in transit between places and not in places. Personally I'd fly in to your first choice city and back from the second choice. I wouldn't fly through Amsterdam and buy separate tickets if you're not going to spend time there - just go directly where you're going. Even if the flight price is cheaper, every time you add more flights/trains to the plan it takes time away from sightseeing (to/from airport, allowing time for security, etc.). If there are any delays or travel drama, you have no wiggle room.

Is the issue with short duration of trip due to 1) getting leave approved by your employer or 2) the amount of vacation time you have available? If it's #2, can you stretch your time over a holiday weekend (e.g., Labor Day)? That might eek out an extra day, but I'd still not try to cover all you listed.

Thanks. I actually found a flight that puts me in Copenhagen from US and I could depart from Stockholm for just a bit more.
It will give me 8 days. And I understand the jet lagged. I did a few similar trips to Asia, and I just try to use jetlag in my favor and start exploring early when possible to avoid crowds. Copenhagen and Stockholm are the must for me.

I can't take more time at once due to work rules, duties as well as personal commitments at home (I'm a single working mom).
My current itinerary puts me in Copenhagen on a Thursday around noon, and I would depart the following Saturday morning from Stockholm.

I was in Copenhagen to take. a cruise in 2019. I believe that it was mid to late September and I did spend a few hours in Stockholm on an excursion.

Late September or early October would be less crowded. Prices would probably have dropped.

I can not remember the weather but I went to my pictures. In Copenhagen, we are wearing jackets but no umbrellas. In Stockholm, I am wearing a sweater only and no rain wear.

Maybe you can book a week in Copenhagen, Then while keeping your hotel room in Copenhagen, go to Stockholm and stay overnight in Stockholm at a hostel or budget hotel before returning to Copenhagen..

In Stockholm, you do want to see the Vasa Museum. In Copenhagen, of course you will be going to Tivoli Gardens but I loved the New Carlsburg Museum also. Both cities are wonderful and beautiful. You are going to have to deal with making choices

Food in Copenhagen is extremely expensive, sometimes shockingly so. I suggest splurging on a. really nice hotel room with a very good breakfast to cut down on food costs.

JoyBBnyc your updated fight choices look much better. Copenhagen central area is easy to reach by train from the airport, you could be out walking around by 2 p.m. I recommend Bike Mike sightseeing tours for a unique perspective and some exercise (I did this the day after I arrived).

Wikipedia's entries for cities usually have a handy climate-summary chart. The monthly averages have limitations for vacation planning (they hide the extremes that can make life unpleasant), but they are useful for comparing weather expectations for different months in the same city or for different cities at the same time.

Focusing on Copenhagen and Stockholm, I'd say the statistics don't show a large amount of rain or a great difference between June and September. I'd expect September to be cooler, but not cold. What is totally predictable, though, is that the days will be much, much shorter in September. Typically there are 50% more hours of sunshine in June than in September--and that's largely attributable to the timing of sunrise and sunset. Weather is unpredictable; the shorter days are a certainty. They bother me; I realize they don't bother most others. But this is an expensive area to travel in, so I enjoyed having extra hours each day to walk around outdoors.

I agree with the other comments that you really don't have enough time to tackle Copenhagen, Oslo and Stockholm, much less to add Gothenburg. I'd choose two of those cities. I haven't been to Copenhagen recently. Of the other three--all of which I liked very much--I think Stockholm calls for the most time because of the number of sights, how spread out they are and the beauty of the city, which makes one inclined to want to walk everywhere.

If you don't want to miss Oslo one option is a "Mini-cruise" from Copenhagen. We did it with my niece last summer. We left Copenhagen around 3PM and arrived into Oslo the next morning had ~7 hours in Oslo and caught the ship back to Copenhagen. The view from the ship sailing north from Copenhagen was beautiful, you will pass "Hamlet's" castle in Helsingør and the next morning's view of the fjord ride into Oslo was equally good. The coast was dotted with norwegian summer cottages. The opera house (we walked the roof), Munch museum where both steps away from where we docked. We walked through the town, saw the royal palace (outside) and went into the city hall and saw the murals. We also took public transport to the ski jump. Obviously, if was a condensed visit but it gave us a great overview. The mini-cruises are not very expensive because you keep the same cabin for the way back. Just something to consider.

https://www.dfds.com/en/passenger-ferries/ferry-crossings/ferry-to-norway/copenhagen-oslo

Thanks all. I updated my itinerary slightly for my early September trip.
I am skipping Oslo but will visit Bergen in between Copenhagen and Stockholm.
Arrival in Copenhagen: Thursday at noon. 3 full days.
Copenhagen-Bergen: Monday midday direct flight
Bergen: 2 full days. One will be all-day fjord cruise/tour (this is a must for me)
Bergen-Stockholm: Thursday late morning direct flight.
Stockholm: 2 1/2 days.
Depart back to USA Sunday morning

Since I will be in Copenhagen over a weekend, are there specific days I should dedicate to the city vs day trip to Helsingor and Frederiksborg Castle? Anything I should book in advance or monitor tickets?

I know 2.5 days in Stockholm not enough but it will give me overview to know if I want to return one day with my family. Not planning to visit archipelago during this trip.

I did Copenhagen/Norway/Stockholm/Estonia/Helsinki in two weeks, single female traveler Aug 23-Sept 7 last year. Weather report said solid rain. I only had one misty day - your mileage may vary! However rain still managed to cancel my train in Norway causing schedule havoc. If you're planning on doing Copenhagen/Oslo, consider the overnight ferry for transportation between the two. Oslo to Stockholm, train is nice if you have time - flight quicker of course. I'd look into direct flights to Copenhagen and out of Stockholm or Oslo just to save time, if you calculate in food/motel you may save money too. As someone said - food is so very expensive over there. Public transportation so easy and cheap, do the daily passes - as far as museums etc, you have to figure how many you want to see vs overall cost to decide which is best value. Best day in Copenhagen was taking the public transport water taxis to various stops.

Ah, I just saw your follow up incl Bergen - fully support that change! I highly recommend the Clarion Admiral Hotel, beautiful comfortable rooms, amazing breakfast and less than a block from where you hop the ferry, as I did to Flam.

Thank you @llczski. I am planning to buy the 3 day pass for Copenhagen as I plan to go out of town and my calculations show savings.
All my long distance travels will be by flight - already booked at great rates. I fly light with carry-on only.
Excited about Bergen and hope the weather is good. I only have 2 days there and one is a full day fjord tour roundtrip from/to Bergen. Thanks for the hotel recommendation.

All hotels I booked in Scandinavia include breakfast with rate. My plan is to not need lunch and just eat small/simple dinner. I don't eat much at night anyway.