# How to track shared money in two currencies

If you share money with someone, and that money lives in more than one currency, you already know the problem. The rent is in one currency, the savings are in another, a card bills in a third, and every spreadsheet you start ends up converting everything into one number that is wrong by the end of the month.

This is common in Latin America, where a lot of people earn, save and spend in both pesos and dollars, but it applies to anyone with a foreign account, a crypto wallet or a trip abroad on a shared card. Here is a way of keeping track that holds up.

## Why one total in one currency misleads

The usual approach is to pick a "main" currency and convert everything into it. It feels tidy, but it hides what actually happened:

- **The total moves on its own.** If the exchange rate changes, your balance changes even though nobody spent anything.
- **You lose what you actually hold.** Knowing you have "the equivalent of 2,000 dollars" does not tell you whether you can pay the rent in pesos this week.
- **Old records stop meaning anything.** A lunch converted at today's rate is not what that lunch cost when you paid for it.

The fix is simple to say: keep each currency as it is, and record the exchange rate of the day next to each movement instead of converting it away.

## Keep one balance per currency

Treat each currency as its own column. If an account holds pesos and dollars, it has two balances, not one. Your overview should read "12,400 UYU and 850 USD", which is what is actually there.

This also makes transfers honest. When you move 100 dollars into pesos, you record it as money leaving the dollar balance and money arriving in the peso balance, at the rate you actually got. Nothing is created or lost in between.

## Record the rate of the day with every movement

You still want to answer questions like "how much did we spend on groceries this year in dollars?". For that, save the exchange rate with every transaction, on the day it happened.

- A rate stored with the transaction never changes afterwards, so the record stays true months later.
- If you changed money at an exchange house or got a card's own rate, write down that rate, not the published one.
- Reports can then add things up in one currency when you ask for it, without rewriting the history.

## Agree on how you record things

Tracking shared money is mostly an agreement between people, and the tool comes second. A few things worth settling early:

- **One place for everything.** If half the expenses live in a chat and the other half in a spreadsheet, nobody trusts either.
- **Record as you go.** A movement written down the same day is accurate. One reconstructed at the end of the month is a guess.
- **Tag by what it was for.** Categories say what kind of expense something is; tags such as "the trip" or "the dog" say what it was for, and they cut across categories and currencies.
- **Everyone can see who recorded what.** Shared money works better when nobody has to ask.

## Frequently asked questions

### Should we convert everything into dollars?

Only when you ask a question that needs one number, such as the total cost of a year. Keep the balances in their own currencies and convert in the report, using the rate stored with each transaction.

### Which exchange rate should we use?

The one you actually got. A card, an exchange house and the official rate all differ; recording the real one is what keeps the record true.

### What if we change money halfway through the month?

Record it as a transfer between two balances: money leaves one currency and arrives in the other at the rate you got. It is not an expense, because the money is still yours.

## Doing it in Contamos

[Contamos](https://contamos.xyz/en) is a shared ledger built for exactly this. Everyone in a team records income, expenses and transfers in one place, and:

- every account can hold several currencies, with a [balance per currency](https://contamos.xyz/en/docs/accounts-and-currencies) instead of one blended total;
- every transaction stores [the exchange rate of its day](https://contamos.xyz/en/docs/exchange-rates), and you can type the rate you actually got;
- [tags](https://contamos.xyz/en/docs/tags) follow money across categories and currencies;
- you can connect [an AI assistant such as Claude or ChatGPT](https://contamos.xyz/en/docs/ai-assistants) and ask it what you spent, or tell it to record a movement for you.

It is free to start, and the [quickstart](https://contamos.xyz/en/docs/quickstart) takes you from signing up to your first transaction in a few minutes.