Two nights is enough for a strong first impression
Kotor is one of the easier Balkan stops to understand quickly because the setting does so much of the work. If you stay in or near the old town or Dobrota, two nights can already give you a very scenic and satisfying trip. You have enough time to enjoy the bay, walk the historic core, and build one good evening around the atmosphere instead of pure logistics.
That said, two nights is still the compact version of Kotor.
Three nights is usually the sweet spot
For most first-time visitors, three nights gives Kotor the right amount of room. The city feels less like a photo stop and more like a proper short stay. You can slow down, choose a better rhythm for the old town, and enjoy the bay without treating every hour like a task. That matters because Kotor works best when the trip feels scenic and calm rather than aggressively efficient.
Three nights is especially strong for couples and shoulder-season travelers.
When a fourth night helps
A fourth night makes the most sense when Kotor is your main scenic base in Montenegro and you want a slower mood. It can also work if you are choosing between old-town atmosphere and quieter bay views and do not want the trip to feel squeezed by arrivals and departures. The value of the extra night is less about extra sights and more about a better pace.
If your trip is short, though, four nights is a luxury rather than a requirement.
The base matters as much as the number of nights
Kotor is one of those destinations where the hotel area changes the whole answer. A well-chosen base can make two or three nights feel perfect. A weak base can make the same trip feel more awkward than it should. That is why the best trip-length decision usually starts with the right part of town, not with the calendar alone.