Almost never. Scandinavia is largely cashless. Even public toilets and street food vendors accept card or phone payments.

Is it worth renting a car?

Only if you are heading deep into the fjords or northern wilderness. Inside the cities, cars are a liability due to expensive parking and congestion.

How to plan a Scandinavian itinerary

Focus on two major cities and one rural region to avoid spending your entire trip on trains or ferries. Allow at least 10 days to cover a meaningful route between Copenhagen, Oslo, and Bergen without rushing.

Pick your primary gateway. Start in Copenhagen. It is the most accessible hub for international flights and allows you to transition into the region via a simple train ride across the Øresund Bridge to Sweden or an overnight ferry to Norway.
Choose your transport backbone. Use the train for the Copenhagen-Stockholm-Oslo triangle. Book tickets exactly 90 days out on SJ (Sweden) or Vy (Norway) sites to secure 'low-price' tickets, which can be 60% cheaper than last-minute fares.
Allocate rural time. Scandinavia is about nature. Dedicate 3 full days to the Norwegian fjords (around Bergen) or the Swedish archipelago. Do not try to see all three countries in under 10 days.
Sync with the light. If you want the Midnight Sun, travel between mid-June and mid-July. For the Northern Lights, go between November and February. Avoid 'shoulder' months like October and April, when it is often wet, dark, and grey.

Do I need cash?: Almost never. Scandinavia is largely cashless. Even public toilets and street food vendors accept card or phone payments.
Is it worth renting a car?: Only if you are heading deep into the fjords or northern wilderness. Inside the cities, cars are a liability due to expensive parking and congestion.