Estimate monthly transit commute cost.
Monthly transit commuting cost is the lower of two routes to the same journeys: paying each fare, or buying the pass. The pay-as-you-go figure uses 4.35 weeks per month rather than four, because twelve four-week months would be forty-eight weeks and understate the year by about eight percent. Whichever is cheaper becomes the headline monthly figure, and the pass saving line — which can be negative — shows how far from the break-even your travel pattern sits.
Pay as you go
Monthly = fare x journeys per day x days per week x 4.35 weeks
Cheaper option
Monthly cost = the lower of pay-as-you-go and the monthly pass price
Substantially. At three commuting days a week most monthly passes stop paying for themselves, which is why the days-per-week field accepts halves — a two-and-a-half-day hybrid pattern is a common break-even case.
Because the pass genuinely costs more than the journeys you will make. That is the useful answer, not an error, and it means paying per journey is correct at your travel frequency.