There is a moment that tells you your budgeting app is single-currency, and it usually arrives about six weeks in. Your net worth drops by a few hundred, you check what you bought, and the answer is nothing. The euro moved. Your money did not go anywhere.
That is not something you can categorise away. Once your money lives in more than one currency, several ordinary questions stop having one answer, and most budgeting tools quietly pick an answer for you without saying which one.
Pick the currency you will spend in, not the one you earn in
Your base currency is the unit everything else gets reported in: budgets, savings goals, net worth. Most people pick the currency their salary arrives in. That is usually the wrong choice.
Pick the currency your money eventually has to cover costs in. If you earn in dollars but live in Lisbon and intend to stay, your rent, your groceries and your eventual pension are euro problems, so euros are your base currency. Your dollar salary is then correctly displayed as what it is: an input that varies in size depending on the exchange rate.
Get this backwards and your finances look stable while your purchasing power moves underneath you. A 6% slide in the euro against the dollar is invisible in a dollar-denominated budget and is a 6% pay cut in the supermarket.
The base currency is a reporting choice, not an instruction to convert anything. You can hold no euros at all and still report in euros.
Convert at report time, never at entry
Record every transaction in the currency you actually paid, and let conversion happen only when totals roll up into a report. This is the rule everything else here depends on.
When you buy groceries in Madrid for 45 euros, the number to record is 45 euros. Not “about 49 dollars, at whatever rate applied that Tuesday.” Convert at entry and you have frozen a rate you will never be able to check again, and you have made your own category history unreadable.
Here is why it matters. Suppose you spend exactly 45 euros on groceries in March and exactly 45 euros in April. You changed nothing. If both were converted at entry, your dollar report might show 49 and then 52, and your grocery category appears to have grown 6%. It did not. You have measured the currency market and labelled it as your behaviour.
Convert only when totals roll up and the original figures stay intact underneath. The euro column says you spent the same both months, which is true. The dollar column says that spending cost you more, which is also true. Two facts, kept separate.
In Spendly this is what the per-account currency is for: each account holds one currency, transactions inherit it from the account, and conversion happens on the way into a report rather than on the way into the ledger.
Budget in the currency the bill arrives in
A rent of 1,200 euros is a fixed cost. Expressed in dollars it is a cost that changes every month for reasons that have nothing to do with your landlord.
Set the target in the currency the bill actually arrives in. Otherwise you spend your time adjusting a budget line to track an exchange rate, which is administration disguised as budgeting, and you will eventually stop doing it.
The same applies to envelopes and sinking funds. A 400 euro grocery envelope should stay a 400 euro grocery envelope regardless of what the dollar did that week. An envelope that silently resizes with the rate is no longer a limit, which was the entire point of it.
Two different problems that get confused
People managing money across borders tend to treat “currency” as one topic. It is two, and the fixes are unrelated.
| Conversion cost | Exposure | |
|---|---|---|
| What it is | Fees and spread you pay to move money between currencies | The value of what you hold moving because the rate moved |
| When it happens | Only when you actually convert | Continuously, whether you touch anything or not |
| How to reduce it | Convert less often and in larger amounts; hold balances in the currencies you spend in | Match what you hold to what you will owe |
| Where you see it | Your transaction list, as a fee or a poor rate | Your net worth, as a change you did not cause |
Conversion cost is a spending problem and you fix it by converting less. Exposure is a balance sheet problem, and converting more often does not fix it at all. Most advice about saving money on exchange rates addresses the first and then gets applied to the second, where it does nothing.
Match the currency of a goal to the currency of the cost
A house deposit in Portugal is a euro goal. Save for it in euros.
If you earn dollars and save that deposit in dollars, you have added a bet on the exchange rate to a plan that did not need one. A 10% move in the wrong direction over two years can erase a year of contributions, and you will have done nothing wrong to deserve it.
This is the one part of multi-currency planning where the answer is usually unambiguous:
- Settling where you live now? Long-term savings in the local currency.
- Children likely to study in your home country? That education fund belongs in the home currency.
- Emergency fund? In the currency of the emergency, which is wherever you actually live. A fund you have to convert during a crisis, at whatever rate that day offers, is smaller than it looks.
- No idea where you will be in ten years? Split it, and be honest that you are choosing not to bet rather than choosing well.
Set each of these as its own savings goal in the currency it will be spent in, and the target stops moving.
Where this breaks
This approach assumes your currencies are reasonably stable against each other and that you can hold accounts in each one. Both assumptions fail in real cases.
If your local currency is losing value quickly, none of the above is the main event. Holding balances in the currency you spend in is normally good advice and is bad advice here. The exposure question overwhelms the conversion cost question, and that is a conversation for someone qualified in your jurisdiction rather than for a budgeting app.
If you cannot practically hold an account in a currency, the per-currency account model degrades into tracking a balance you do not really control. It still beats a single-currency budget, but the advice to hold what you spend is not available to you.
If one currency is more than about 90% of your financial life, the extra structure is probably not worth it. A holiday twice a year does not make you a multi-currency case. Log the trip, let it convert, move on.
Tax is not covered by any of this. Some countries tax realised currency gains, and the moment you convert can be a taxable event. A budgeting app models your money, not your tax residency.
What to actually do
If you are setting this up from scratch, the order matters:
- Pick the base currency by where the money will be spent, not where it is earned.
- Create one account per currency you hold, each with its real current balance.
- Log transactions in their original currency and never convert by hand.
- Set budgets and envelopes in the currency each bill arrives in.
- Give every savings goal the currency of the thing it buys.
- Read net worth changes in two parts: what you saved, and what the rate did.
The last one takes longest to build and is worth the most. A month where you saved well and the currency moved against you is a good month with bad weather. If your tools present those as one number, you will eventually draw the wrong conclusion about your own behaviour.
Common questions
What should I pick as my base currency?
Pick the currency you will spend the money in, not the one you earn it in. If you plan to settle where you live now, that is your base currency even if your salary arrives in another. The base currency is the unit your net worth is honest in, so it should match the costs your money eventually has to cover.
Should I convert foreign transactions when I record them?
No. Record the amount you actually paid in the currency you actually paid it, and let the app convert only when it rolls totals up for reporting. Converting at entry freezes a rate you can never check afterwards and makes month-to-month category comparisons meaningless, because a change in the exchange rate looks identical to a change in your spending.
Why does my net worth change when I have not spent anything?
Because part of it is held in a currency other than your base currency. When the exchange rate moves, the base currency value of those holdings moves with it. This is real rather than an accounting artefact, but it is a different event from spending or saving and is worth reading as a separate line rather than as a change in your behaviour.
Which currency should I save a goal in?
The currency the goal will be paid in. A deposit on a house in Portugal is a euro goal, so save it in euros even if you earn in dollars. Matching the currency of the saving to the currency of the future cost removes exchange rate risk from the goal. Save in the wrong currency and a rate move can undo a year of contributions.
Related reading
- Does YNAB support multiple currencies? covers the one-budget-per-currency limit and what the workarounds cost
- Budgeting methods across currencies looks at which popular methods survive contact with a second currency
- Budgeting as a cross-border couple handles two incomes in two currencies