RoomMate

RoomMate is a full-stack expense-splitting app built for people sharing a room or flat, the kind of setup where rent, water, electricity, and groceries get divided among however many people happen to be living there, and a simple even split never quite matches reality.

The problem

Most bill-splitting apps assume every expense divides evenly across everyone, every time. Real shared housing doesn't work that way:

• Someone doesn't eat meat, so groceries with meat shouldn't split across everyone.
• Two roommates share one wallet, one "covers" the other, so their share should redirect, not double-count.
• Some purchases (like a gas refill) get paid for in cash on the spot, there's no debt to track, but it should still show up in spending history.
• Billing cycles aren't the calendar month, every household picks its own cycle-end date.

RoomMate handles all of this as first-class features, not edge cases.

Key features

• Households with 6-character invite codes
• Custom billing cycles with owner-triggered, member-approved close requests
• Fixed bills (rent, water, electricity) tracked historically
• Itemized, participant-scoped expenses, choose exactly who each purchase splits among
• One-directional coverage relationships (pays_for), enforced server-side
• Settled-on-the-spot expenses that count in spending stats without creating phantom debt
• Real settle-up balances via a greedy debt-simplification algorithm
• Immutable itemized receipts, exportable as PDF/PNG
• Personal + shared dashboards with Recharts insights
• Offline-first shopping mode with background sync
• Installable PWA

Notable engineering details

• Row Level Security on every table, with a few SECURITY DEFINER RPCs for the cases plain RLS can't express safely (e.g. joining a household by invite code).
• Split calculations are computed once, server-side, and reused consistently across every view, an early version duplicated this logic per-view, which caused numbers to visibly disagree with each other until it was consolidated into one source of truth.
• Deployed functions are region-pinned to match the database region, cutting the cross-continental round-trip latency that was previously the dominant cause of slow page loads.