City comparisons only work when you compare like-for-like. Both columns here use the same five line items — accommodation, food, local transport, activities and miscellaneous — and default to mid-range, shoulder season, which is the most honest baseline for a typical traveller.
Accommodation alone drives 50–60% of the gap between most city pairs. Food is the second largest swing, then activities. Transport and miscellaneous rarely move the overall total by more than 10%. If two cities look surprisingly close on this page, it's almost always because their accommodation markets are at the same price point.
Porto is about $277 cheaper per day than Reykjavik at mid-range in shoulder season — roughly 50% lower. Across a seven-day trip that's about $1939 back in your pocket per person before flights.
Most of the gap comes from accommodation: Reykjavik's nightly rates run materially above Porto's. Food and activities account for the rest. See the full breakdowns on the Reykjavik and Porto pages.