How to track your money when you earn in one currency and spend in another

If you earn in one currency and spend in another, you already know the problem isn't writing things down. The problem is that the sum means nothing. A total that mixes two currencies is a number that doesn't exist, and converting by hand means looking up each day's rate.

Here's how to track it in a way that's useful for deciding, not just for recording.

The mistake: converting on the way in and dropping the original

The quickest approach is to convert everything into one currency as you log it and throw away the original figure. It works until the first month you want to review something.

When you store only "I spent 47,000 pesos", you've lost the fact that the expense was 40 dollars. Those are two different things: rent priced in dollars goes up in pesos without you changing anything about your life, and if you only kept pesos you have no way to tell "I spent more" apart from "the exchange rate moved".

The practical rule: store every expense in the currency you actually paid in, and let the conversion be a view, not the data.

Which rate to use

The one from the day you made the expense, not today's. It sounds obvious and almost no spreadsheet does it, because in a spreadsheet it's painful.

The consequence of using today's rate is that a month that's already closed changes size every time you open it. January stops being comparable to February, because the difference between them is no longer how much you spent: it's how much the rate moved between January and the moment you're looking. For making a decision, that's useless.

That's why the conversion has to be frozen when the expense is logged. It's one of those decisions that looks like a technical detail and is actually the difference between numbers that work and numbers that don't.

Which currency to read the total in

It depends on the question, which is why you want to be able to switch without touching the data:

• The currency you live in, to understand your real cost of living and make day-to-day decisions.
• The currency you're paid in, to compare against your income and know what share of it is going out.

Both views are useful and answer different questions. If you have to pick one forever, you're losing half the picture.

Shared expenses make it obvious

This is where it all comes to a head. A trip where the hotel was paid in reais, the flights in dollars and the meals in pesos can't be divided by hand without an afternoon of work — which is exactly the moment nobody feels like doing it.

The same thing happens, more slowly, in a home where rent is in dollars and groceries in pesos: if the two aren't converted on the same basis, the balance between two people comes out wrong and nobody's quite sure why.

How Kesef handles it

Each movement is stored in the currency you paid in — rent in dollars stays in dollars, coffee in pesos stays in pesos — and separately you choose which currency to see totals in. Changing that view doesn't alter any movement.

The conversion uses the rate from the moment you record the expense and stays fixed: a closed month doesn't change size afterwards. It's more than 60 currencies, and it's on the free plan.

Groups follow the same rule: each shared expense is converted as it's logged and the balance stays in a single currency, which is what keeps a trip with expenses in three currencies adding up.

Kesef is free, on iPhone and Android

Shared expenses with no cap, 60+ currencies, and the numbers explained.