Three full days is the honest answer. That is long enough to walk the colonial-era southern tip, cross the old mill districts in the middle, and get north into the suburbs where the overwhelming majority of the city's population actually lives and eats. Two days can be done, but you will spend a punishing share of them in a stationary car. A week is more than the city asks of a first visit, unless you are here for work anyway.
A fourth day is the one worth negotiating for, because it buys the thing three-day visitors almost always sacrifice: a boat across the harbour to Elephanta, or a train north to a forest full of Buddhist caves. Both are genuine excursions, both eat most of a day, and neither can be squeezed into a morning.
The reason the maths works out this way has little to do with how many sights there are. It is the shape of the place. Mumbai occupies a narrow strip of reclaimed islands running roughly forty kilometres north to south, and in stretches it is barely three kilometres across. Everything is stacked along that one axis. An itinerary that pinballs between Colaba in the far south and Juhu in the north-west and back again in a single day is not an itinerary; it is a commute with sightseeing attached. So the three days below are arranged as a slow migration northward. You start at the tip, and you never double back.
Getting around, which is most of the trip
The ground genuinely shifted here in October 2025, when the final underground stretch of Metro Line 3 opened and the Aqua Line began running its full length, from Cuffe Parade at the southern tip all the way to Aarey in the north. It is the city's first almost entirely underground line, with 27 stations, and it runs directly beneath the western spine that every visitor spends their time on: Churchgate, Hutatma Chowk, Girgaon, Mumbai Central, Mahalaxmi, Worli, Siddhivinayak, Dadar, Dharavi, and onward past both airport terminals. Fares are modest, typically somewhere between a handful of rupees and about eighty for the longest hops. Used properly, it removes the single largest variable from a Mumbai day, which is surface traffic.
It does not solve everything. The line serves the eastern side of Bandra and the business district at BKC, so for Bandra West, where the Ranwar lanes and the sea promenade are, you still want the Western Railway suburban train to Bandra station or simply a cab. Those suburban trains are the city's circulatory system and are worth riding once, in first class, which costs several times the second-class fare and is still cheap by any visiting standard. Ride them outside the rush, broadly avoiding the late-morning and early-evening peaks, when carriages are packed to a degree that is genuinely unsafe for anyone unfamiliar with how boarding works. Women travelling alone should use the ladies' compartments, which are clearly marked and much calmer.
Two other quirks matter. Autorickshaws are not permitted in the island city south of the Mahim and Sion boundary, so anywhere in the southern half of this itinerary you are looking at a black-and-yellow taxi or an app cab; north of that line the auto is quicker and cheaper than either. And the Coastal Road, opened in stages through 2024, now connects Marine Drive to Worli and on to the Bandra-Worli Sea Link. On the southern stretch it is toll-free, and a run that used to consume the better part of an hour in the evening now takes ten or fifteen minutes. It also came with a long sea-facing promenade, which is a pleasant thing to have discovered by accident.