Budgets Break the Moment the Trip Starts
Shoestring plans trips against a small budget. The interesting problem is what happens on day two, when reality disagrees with the plan.
Shoestring is for planning trips you cannot really afford. Epic trips, tiny budgets. You set a total, you sketch the days, and it tells you whether the thing you want is actually possible.
Building the planner was straightforward. What I got wrong was assuming anyone would follow it.
A budget is a forecast, not a ledger
Most budgeting tools are accountants. They record what you spent and then report, after the fact, that you spent too much. That is fine for a household, where next month is another try.
A trip is not like that. It has a hard end date and a fixed pot, so the only question that matters is forward-looking: given what I have already burned, what can I still do? Telling someone on day three that they are 18% over is technically true and completely useless. They know. They were there.
The plan has to bend instead of break
The failure mode is a plan that assumes compliance. You overspend on day two, which everybody does, because a trip is precisely the situation where the unexpected thing is the point. If the tool responds by turning the whole plan red, you stop opening it, and it was giving you the least useful information at the exact moment you most needed help.
So an overspend is not a violation. It is new information, and the correct response is to reprice the rest of the trip against what is actually left. Fewer paid activities, or one cheaper night, or the nice dinner moves from Thursday to nowhere. The plan changes. The trip survives.
That reframing is the whole product. Not “you broke the rules” but “here is what still fits”.
What I took from it
A planning tool that only works when you comply is a guilt machine. People abandon those on day two, which is also the first day they are worth anything.
Forward-looking beats backward-looking when the deadline is fixed. Nobody needs a report on a trip they are currently on.
Design for the deviation, not the plan. The plan is the easy state. Every interesting product decision lives in what happens after it stops being true.