### MBTA passes math

2017-Apr-30, Sunday 08:11Four 7 day passes would be $85; a monthly pass is $84.50. So that makes sense too. Or does it? Say you have three weeks of vacation, and leave town for them; maybe you'd save money by just cycling 7 day passes, and skipping the weeks you're gone.

I approached the math from a couple different angles, but this presentation seems best: a month pass costs about the same as 4 weeks, so 12 monthly passes covers the year for the cost of 48 weekly passes. Even if you skip 3 weeks, you'd still have to buy 49 passes... plus covering that extra day (or two, if leap) in the year. So go monthly!

Though, having been using 7 day passes, I noticed that they actually shuffle forward. If I buy one on Monday morning, the next Monday I can leave a bit earlier and still use it, buying (or activating) my next pass Monday evening. And so on. The effect is that you end up covering 30 days for the cost of 4 passes, as each one picks up an extra "half-day" commute. And if you shuffled into buying a pass on a weekend, well, maybe you could skip travel that day and save an extra day.

Of course, there's a week's worth of 31 day months, so there's that -- you're not quite getting a month's worth for 4 passes.

It's nice doing estimations in my head, but at some point you have to turn to a calculator for precision. A year's worth of monthly passes is $1014. If you cover 30 days with 4 weekly passes, that's $85 per 'month', and $1020 to cover 360 days, with 5 more days to finagle. OTOH, if you can skip 3 weeks, you'd spend just $956.14 in a year, saving $57.75. Or $42.57, if you threw in 5/7 of another pass for the extra days.

Of course, that assumes you can maintain the shuffle. Weekends offer skipping a day, but a regular weekend thing might pin you down. Say I activate a pass at 8pm Sunday to go to Grendel's; the next week I might leave earlier, but I'd still have to activate a new one at 11:30 to get home. The week after that I could leave Grendel's a bit earlier, activating the next pass on Monday morning... okay, it still works, though Sunday feels a bit sticky due to the short 'commute'.

Of course, the monthly pass means not having to buy stuff every week, nor worry once a week about the timing of when you do things. OTOH, saving $40 to 60... well, it's not a ton, but it's not trivial either; 40/1014 is 4%.

Extra thought: if you really use the weekends on your one-week vacations, you could save another 2 days each, or 6 days total, in effect skipping another week.

As for me, if I had today off I'd probably just go monthly. Annoyingly, I probably have 4 or 5 trips to make today. Cash today and monthly tomorrow, or weekly today?

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Meanwhile, the $12 daily pass is hard to justify unless you run around a lot. Even for a tourist spending $2.75 per trip via CharlieTicket, it costs more than 4 trips -- though if you're doing train/bus transfers that becomes a lot easier to justify, since the Tickets don't give a free transfer. But even then you'd d need bus/train, bus/train, and one more trip. For a Card user you'd need to make 6 independent trips to make a day pass economical. Most likely use case would be having to make multiple quick trips along a train line.