Best way down Rhine from Dusseldorf to Frankfort in 1 or 2 days

Type "Middle Rhine" into the search box, top center. Most posters recommend taking a KD boat from Bingen to Bacharach or St. Goar. Timetables are seasonal, and not all year round. Download them from the KD site. The train is so fast and cheap that it's not an issue. 15% KD discount with same-day train ticket.

Edit: I might note that while Dusseldorf and Cologne are wonderful visits, they are not ideal bases for boating the Middle Rhine. Even when we were sleeping near Koblenz, that was not ideal - but it was a reasonable train daytrip. It cannot be overstated how much faster the train is than the boat. The train saves you time for other sightseeing. The DOWNSTREAM boat gives a wonderful view, and (look at the schedule ... ) not TOO fast to enjoy it.

The OP should note that there are train lines on both sides of the Rhine. But the DB ticket site is reliable and easy to use, and you don't have to "buy" the ticket to look at the scheduling. However, it can be tedious to buy same-day tickets at a station that ONLY has a machine to sell train tickets.

When I type in on the DB website the route of Dusseldorf to Koblenz or St. Goar, most of the routes say that the trains don't operate every day in October 2019 when we will be traveling. I am trying to make sure I get to St. Goar to be able to make the one upstream Rhine cruise that day, but how will I know for sure if the trains will be running to get me to St. Goar?

If you put your actual travel date on the DB website, you will only see trains that are actually running.

"...the one upstream Rhine cruise that day..."

There may be some confusion on your part about the schedule. KD has 5 upstream boats (from St. Goar to Bingen or Rüdesheim) every day through October 13. There are 4 upstream boats every day from October 14-20.

In case you are cruising after October 20, Bingen-Rüdesheimer cruises offers 2 boats every day all the way through Nov. 3, at 13:15 and 15:15 from St. Goar to Bingen (or R'heim.)

There is only ONE boat per day if you have it in mind to cruise upstream all the way to Mainz with KD. Is that what you are thinking? This is a lot of expensive and mostly unnecessary river cruising because the part from Bingen to Mainz is a lot less interesting (which is why there's only one boat.) It's nothing I'd ever recommend. I would get off the boat in Bingen - or in Rüdesheim, where you can take a direct regional train into Frankfurt.

It is extremely unlikely that you will have any trouble getting to St. Goar. I sampled October 19 and clicked on "only local transport" to find regional trains you might use with day passes. Using these slower trains requires 3 hours with one change of train in Cologne. Beginning at 5:58 a.m., they depart hourly at :58 after the hour. The fare is €36.20 each, or €52 for two (day pass.)

Now, there is a footnote for this itinerary... "runs not every day, 26. Aug until 14. Dec 2019." But this note is just telling you that there might be one or a few days between these dates when the usual departure at XX:58 is not running. In other words, if your actual travel date is October 29, don't count on the schedule you just pulled up for October 19. But that statement does not mean your train on October 19 isn't running. It is, or it would not be on the schedule for October. Get it? The footnote is just a heads up to regular users of the trains that they need to check the schedules for their specific date rather than rely on what happens for 99% of the time during the course of this 4 month period.

If you want to re-post with your travel date and your cruise boat destination, you can get some help from those of us who are more familiar with the route, the boat schedules, the DB site, and ticketing options.

I am sorry for the confusion. I would like to travel from Dusseldorf to Bingen by train, then take the KD boat from Bingen to St. Goar, then visit the castle in St. Goar, and return by train to Dusseldorf all in one day. My options are to accomplish this on Sunday, October 20th or Monday October 21st in 2019. For many of the train options on the Bahn.de website it says train “runs not every day, 26. Aug until 14. Dec.”. I need a more definite schedule than that, please.

katborch, thank you for that easy to understand post with details. I don't see the omitted-train warnings you see to Bingen. I see, even on Sunday, lots of trains, taking from two to three hours (Duss-Bingen). Departures on Sunday are at :27 and :47. We should have noted that there are two stations in Bingen, Bingen Stadt (not exactly "downtown"!!) being closer to the KD dock.

I do see a warning for some trains Boppard-Frankfurt, like "IC 2027: Koblenz Hbf-> Frankfurt (Main) Hbf: construction work. There will be changes to the timetable of the train. Please check your connection again shortly before the trip." There is at least one train an hour that doesn't have the warning. Read on:

When I expand the train details, I get a good clue: The trains with the warning are VIA KOBLENZ, which is the "wrong way" (but not very far.) The trains without the warning are VIA MAINZ, in the "right" direction. I suspect that they may be using the other side of the Rhine for construction on one side, but I'm making that up. As an experienced traveler, I would maybe buy a non-specific train ticket to Frankfurt, so I could take any train that day. But if you are meeting an airline departure in Frankfurt then you would be right to worry a bit. This is (partly) the price of traveling in shoulder-season.

Since you are going back to Dusseldorf, I don't see much to worry about.

Note that 21 October 2019 is the day KD changes from the Off-Season timetable to the microscopic Winter boat timetable.

You can buy a ticket today for October 20, for 19.90 EUR, Duesseldorf Hbf to Bingen Stadt Bf, departing at 7:51 am getting to Bingen Stadt Bf at 10:26, giving plenty of time to walk to the dock. You could also skip the connection and walk to the dock from Bingen Hbf, which is a bit longer walk. The next KD boat is at 11:30. That one would get you to St Goar at 12:55. Then trains back to Duesseldorf at 2, 3, 4 pm.costing 19.90 to 23.90 EUR bought now, or 40 EUR for anytime tickets.
www.bahn.com for schedule, prices, ticket purchase.

I would like to travel from Dusseldorf to Bingen by train, then take
the KD boat from Bingen to St. Goar, then visit the castle in St.
Goar, and return by train to Dusseldorf all in one day.

I'm glad you see why your title might be confusing...
"Best way down Rhine from Dusseldorf to Frankfort in 1 or 2 days"

For many of the train options on the Bahn.de website it says train
“runs not every day, 26. Aug until 14. Dec.”. I need a more definite
schedule than that, please.

I addressed this concern of yours in my last post. It is not a concern. Please re-read the next-to-last paragraph in that post.

To travel with KD, you should go on Sunday, the last day of KD operation for the summer. (But you can use Bingen-Rüdesheimer boats on either Sunday or Monday.)

B-R boat schedule: https://www.bingen-ruedesheimer.de/pub/media/wysiwyg/Fahrplan_2019/Fahrplan_de/Fahrplan_Loreleyfahrt.pdf

This train ticket is likely your cheapest option for the round trip, €44. On Sunday, you can use this ticket at any hour of the day (not so on Monday - only after 9 am on Mondays.) You can use it on ANY of the regional trains that same day. You do NOT have to pre-purchase this ticket - just buy it at the station in D'dorf:

https://www.bahn.com/en/view/offers/regional/day-ticket-for-germany.shtml

Note that the saver fare tickets recommended by other posters require you to use specific trains on specific dates at specific times. With the day pass option, you do not have to choose NOW what day you will do this trip. You can decide that once you are there, based on the weather or other factors - and if you miss a train, you will not forfeit your day pass (like you will with the saver fares.)

This is what I would do on Sunday:

Lv. D'dorf 8:58, ar. Bingen 11:49. Have lunch in Bingen and get your cruise ticket. Board 13:15 boat north. Ar. 15:05 in St. Goar. Tour Rheinfels. Depart St. Goar by train 18:00, ar. D'dorf 21:01, one change of train w/ 26-min layover at Köln Messe/Deutz. No construction or other interruptions.

If you want to find this and other regional train connections, you need to do as I suggested before - click on "only local transport" under "Connections - means of transport." But in truth you do not need to find it because you do not need to pre-purchase any tickets. These trains are on the schedule and they will be running on Sunday October 20.

Now, if you go on MONDAY, I would use the exact same plan. The trains run on the same schedule. So do the B-R boats. The only difference will be that you cannot get on that train in D'dorf at 8:58 am with only that day pass - it's not valid until 9 on weekdays. So you need one small supplemental ticket. In addition to the day pass, buy a local "VRR" transport ticket at the station for Düsseldorf Hbf > Düsseldorf-Benrath (€2.90) With this ticket, you can board the same 8:58 train and ride for two minutes until your day pass kicks in.

The day pass gives you the flexibility to ride any of the regional trains you like that same day. If you want to leave D'dorf earlier than 8:58, you can. If you want to leave St. Goar earlier than 18:00, just get on ANY northbound regional trains. The ticket machines at the St. Goar station will show you a schedule, or you can print out several possible regional train schedules in advance of your journey.

If you put in Oct 20 or 21 and you get a schedule for a connection that day, and it says "runs not every day", it does run on the date you put in. if it didn't run that day, the Bahn wouldn't show the connection on that day. One of those notes even says what days it doesn't run - "not 1. Sep , [and] 15. until 17. Oct 2019". That's does not run "on Sept 1, or from Oct 15 through Oct 17". Remember, European date format puts the numerical date before the month.

I am trying to make sure I get to St. Goar to be able to make the one upstream Rhine cruise that day,

I highly recommend that you not do an upstream cruise, as against the current the boats go excruciatingly slow. And, BTW, the KD dock is at Bingen Stadtbahnhof. Don't try to go from Bingen Hauptbahnhof.

Bingen Hbf is a bit more than a mile walk to the KD dock, while it is 1/4 mile from Bingen Stadt Bf. IC trains coming from Duesseldorf stop at Bingen Hbf, but not at Bingen Stadt Bf, so you need to connect to a local train to get there. The 7:51 am EC train from Duesseldorf stops at Bingen Hbf at 9:51, then its a 33 minute wait for the local train to go the last mile. Since you will have 1 1/2 hours to kill before the next KD boat, you could take a pleasant walk across the Nahe river bridge and walk along the Rhine to the dock. That assumes light or no luggage and nice weather. Cold and rainy, stay warm in the Hbf and wait for the connecting train.

There is nothing wrong with riding this ship upstream. It is not excruciatingly slow. That makes it sound painful. It isn't. It can be quite relaxing and lovely. Have gone this direction a number of times and found it enjoyable. If this fits your plan better, go for it. Have a glass or two of Riesling, take lots of photos, have a snack.

The merits or drawbacks of cruising upstream are not relevant here. The OP made it clear that she wants to cruise downstream:

"I would like to travel from Dusseldorf to Bingen by train, then take the KD boat from Bingen to St. Goar, then visit the castle in St. Goar, and return by train to Dusseldorf all in one day."

(The previous mention of an "upstream" plan wrongly assumed "north" = "upstream" - this happens all the time here.)

I appreciate all of the detailed responses to my question. Truthfully, I don't care which way I go--upstream or downstream. My original post indicated upstream, but I was worried about time constraints and changed my mind to say downstream. If I can manage either way in a day from Dusseldorf to Bingen and back (no longer interested in ending up in Frankfort, then I will be very happy. I see that is possible either upstream or downstream. Thank you.