The Paris Museum Pass is sold as an obvious saving. Whether it is depends on a number most buyers never calculate.
The break-even
The pass costs roughly the price of three to four major site admissions, depending on the duration bought.
So it pays off from the fourth site onward — and most visitors manage two, sometimes three, major museums a day before fatigue sets in.
A two-day pass therefore needs a genuinely museum-heavy two days. A visitor doing the Louvre, Orsay and one other breaks roughly even and has saved nothing but queue time.
Count your actual list against current prices. Five minutes of arithmetic settles it.
What it does not cover
This is where people are caught out.
The Eiffel Tower. Not included, and it is what many visitors most want.
Most temporary exhibitions, which are often the reason to visit a particular museum in a given month.
Boat trips, the Catacombs on some terms, and various smaller attractions.
The reservation trap
The pass does not replace a timed reservation.
The Louvre and several other sites require one, pass or not, and slots fill in peak periods. Turning up with a pass and no booking is a common and entirely avoidable frustration.
Book the reservation as soon as you have the pass.
What is free
Permanent collections in municipal museums — the Musée Carnavalet on the history of Paris, the Petit Palais, the Musée d'Art Moderne — are free year round. Several are excellent and none appear on standard itineraries.
First Sundays. Several national museums are free on the first Sunday of the month, though the scheme has narrowed and some now apply it only in low season. Check each museum's current policy, and expect crowds where it applies.
Under-26 EU residents enter national museums free, which includes the Louvre and Orsay.
Père Lachaise, the Sacré-Cœur, Notre-Dame's exterior, the covered passages, the parks and the Seine. Free, and among the best of Paris.
The other cards
Several Paris passes exist and they are not the same product. Some bundle transport, some bundle attractions, some bundle both at a considerably higher price.
Transport is cheap in Paris — a carnet of metro tickets or a Navigo pass costs little. Bundling it into an attractions card rarely improves the maths.
Compare the bundle price against buying the two or three things you actually want, separately. The bundle wins less often than it appears to.
Where the real savings are
Eat lunch, not dinner. The formule midi — two courses at lunch — costs roughly half the evening equivalent at the same restaurant.
Stand at the bar for coffee. Seated on a terrace costs two or three times as much, and the two prices are legally posted.
Go in winter. Accommodation drops substantially, the museums are empty, and the city is arguably better for it.