🛠 Building JAB47: making sense of multiple currencies

We were working through a scenario: someone has accounts and cards in different currencies, then spends in several more while travelling. Some purchases go on a card; others are paid in cash picked up at a currency exchange. We want them to be able to make sense of their spending and balances in the app.

As we broke it down, the questions kept coming.

What currency was the purchase priced in, and which currency was actually charged? Why does the rate on the bank transaction differ from the one the person saw before paying? What about cash exchanged at yet another rate? And what exactly do they expect to see when they ask, “How much did I spend on this trip?”

“The exchange rate” quickly stopped being one straightforward number, too. There’s an official reference rate, the bank’s rate, the conversion offered at checkout, and the rate at the currency exchange. Those numbers can differ quite a bit, even for the same currency pair.

The app needs to collect, store, and process all those amounts and transactions. Then turn them into something a person can understand. They came to find out how much they spent and how much they have left, without having to untangle currency conversions themselves.

That’s how a single line in a feature list—“multiple currencies”—becomes a substantial development task. And this is just fiat money. We haven’t even brought crypto into this scenario yet.

We’ve come up with a solution we’re really happy with, and we’re now bringing it to life in JAB47. You’ll see how we’ve tackled it in the finished app 😉 Here, we’ll keep sharing the challenges we encounter along the way and what solving them will mean for you.