Case study · Shared expenses & bill splitting · iPhone
AllSquare
A bill-splitting app with no daily limits and no ads, backed by a ledger that adds up to the cent.
The challenge
Splitting shared costs sounds simple until real life shows up: several people pay for one dinner, a trip mixes currencies, someone adds an expense on a plane, and a cent has to go somewhere when $100 is split three ways. Popular apps in this space limit how many expenses free users can add per day and show ads.
What we built
- A native iPhone app in Swift and SwiftUI with every way to split: equally, exact amounts, percentages, shares, adjustments, item by item and multiple payers.
- Money stored as whole minor units (cents) everywhere, never floating point, so every split adds up exactly and leftover cents rotate fairly between people.
- Debt simplification that settles a group in the fewest payments without changing anyone's total, kept separately for each of 50+ currencies.
- Offline entry with a sync outbox: expenses added without a connection sync on reconnect, with a field-by-field merge when two people edit the same expense.
- A TypeScript backend (Fastify, PostgreSQL) with push notifications, recurring bills, receipts, comments, an activity feed and invite links.
- English and Bengali, with Dark Mode, Dynamic Type and VoiceOver built in.
Technology
- Swift 6
- SwiftUI
- SwiftData
- TypeScript
- Fastify
- PostgreSQL
- APNs
The result
A complete expense-sharing product, coming soon to the App Store, free with no daily limits and no ads.
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