Money that has to add up: how Zimmati keeps group balances honest

If three friends split $100 equally, who pays the missing cent? Expense apps quietly fall apart on questions like that, and over a long trip the small errors add up to an argument.

Zimmati, our expense-splitting app, is built on three rules.

1. Count money in whole cents

Every amount is stored as whole cents, never as a decimal that can drift. When a bill does not divide evenly, the leftover cents are assigned in a fixed, predictable way, so the parts always add up to the total.

2. Never store a balance

The balance on screen is calculated from the expenses and payments that actually happened. Edit an expense or record a payment and the balance follows. There is no stored number that can fall out of step with the history.

3. Fewer payments to settle up

At the end, Zimmati simplifies who pays whom, matching the biggest debts against the biggest credits, so a messy chain of debts becomes a few simple transfers.

None of this is visible in a screenshot. It is exactly the kind of work we do for clients whose products handle money that has to stay correct.