How to split expenses in multiple currencies (without wrong balances)

Auto-converting every expense into one currency bakes an invented exchange rate into your group's debts. Tracking each currency separately avoids it.

The dependable way to split expenses in multiple currencies is to keep each currency separate: euro expenses stay in euros, dollar expenses stay in dollars, and the group settles each currency on its own. Converting everything into one currency with an automatic exchange rate looks convenient, but it builds the group's debts on a rate nobody agreed to — and that rate keeps moving after the expense is recorded.

Why does forced conversion go wrong?

Three separate problems stack on top of each other.

The rate is invented

Which rate, exactly? The mid-market rate at the moment of entry? Your bank's rate with its markup? The rate your card actually applied when the charge settled three days later? An app has to pick one — and whichever it picks is almost never the rate anyone in the group actually paid.

The rate drifts

A trip lasts days; the debts often last weeks. If the app converts at entry time, two identical $20 taxis on different days create different euro debts. If it converts at view time, your balance changes overnight while nobody spent anything. Either way, the longer the group takes to settle, the further the numbers wander from what happened.

Nobody agreed to it

Money friction in groups is rarely about arithmetic — it's about legitimacy. A converted balance is a number nobody can recompute from what they remember paying, so it gets contested. A per-currency balance is checkable by anyone with the receipts: every cent traces back to a real payment in a real currency.

What does per-currency tracking look like?

Each currency gets its own ledger. You can owe €30 and be owed $15 at the same time — both numbers are true, and neither is blended into the other. When the group settles, it settles per currency: euro debts with a euro transfer, dollar debts in dollars. And if someone would rather clear everything in one go, the group agrees on a rate at that moment — once, out loud, on numbers everyone can see.

A worked example: Lisbon, with a dollar detour

Ana, Ben and Cami spend a weekend in Lisbon, and one activity gets charged in dollars. Two expenses:

• Dinner in Alfama: €90.00, paid by Ana, split three ways.
• Boat tour: $45.00, paid by Ben, split three ways.

Tracked per currency, every balance is exact and nobody looked up an exchange rate:

Settling is two small rounds: Ben and Cami each send Ana €30, then Ana and Cami each send Ben $15. Every number in that plan is an amount someone actually paid — not an estimate filtered through a rate.

Now run the same trip through auto-conversion at, say, 1 USD = 0.90 EUR on the day of the tour. Ben's $45 becomes €40.50 and everyone owes him €13.50. If the rate is 0.93 by settle-up day, that conversion quietly gave or took real cents from each person. Across two expenses it's cents; across a two-week trip with dozens of entries it adds up — and worse, no one can audit it afterwards.

When is converting actually fine?

This isn't a crusade against conversion — it's about where the conversion happens. Converting is perfectly reasonable when it happens once, at the end, at a rate the group explicitly picks. The trip is over, the balances are final, and someone says: “let's settle everything at the rate my bank charged — 0.92”. One agreed number, applied once, in the open. The trouble is only the automatic, per-expense, continuously-shifting rate baked silently into balances.

It also matters less when the foreign amounts are small: if a euro trip has one $12 expense, any sane rate lands within a few cents and nobody minds. The failure mode needs volume — many expenses, mixed currencies, time between spending and settling.

How does Deudin handle multiple currencies?

Deudin tracks balances per currency by design: no exchange rate ever touches your data. The group screen shows one balance per currency, and the settle-up suggestion computes the fewest transfers within each currency — so the Lisbon group above sees its two-round plan directly. It works fully offline too, which matters in the exact places where your card starts charging in someone else's currency. Create a group free, or see how it plays out on trips.

The trade-off is real and worth naming: Deudin won't show you a single converted total, because we'd have to invent the rate to do it. If a one-number total matters more to you than rate-free balances, apps that convert are the better fit — Tricount and Splid convert automatically, Settle Up fetches daily rates, and Splitwise offers conversion in its Pro plan.

Facts checked July 2026. Competitor conversion behavior is taken from each app's public feature descriptions.