Most travel advice assumes you’ll use your card for most things and only carry a small amount of local cash for situations where cards aren’t accepted. That’s a reasonable strategy in major cities with reliable card infrastructure.
It doesn’t describe how travel actually works for most people. Markets, small restaurants, local transport, rural areas, countries where cash is still the dominant payment method — the moment you leave the predictable tourist circuit, cash becomes unavoidable. And when you’re moving between countries, you end up managing multiple currencies at once, each in a separate pocket or envelope, with no obvious way to know where you stand.
The problem with mixing currencies mentally
The human brain is not good at holding multiple running balances in different denominations simultaneously. You might have a rough sense of how many euros you have left, and a rougher sense of your sterling, and almost no sense of what those amounts represent in terms of your remaining budget.
Currency conversion makes this worse. If you’re spending euros but thinking in dollars, every transaction requires a mental calculation — and that calculation is approximate, and approximation stacks up across dozens of transactions until your estimate is meaningfully wrong.
Most travellers deal with this by ignoring the problem until they run out of money in one currency, then withdrawing more. This works, but it’s not really tracking. You have no idea what you spent in each country, what you spent on, or whether you stayed within any kind of budget.
Separate pools for separate currencies
The most effective approach is to treat each currency as a completely separate cash pool. Not a mental category — an actual distinct record that you manage independently.
This sounds obvious, but it changes the tracking problem significantly. Instead of trying to maintain a unified multi-currency ledger with constant conversions, you simply maintain a record for each currency in that currency. Your euros are tracked in euros. Your dollars are tracked in dollars. Conversion only matters if you’re trying to see your total expenditure across everything, which is a summary question you can ask at the end of the trip rather than something you need to calculate transaction by transaction.
When you withdraw cash in a new currency, that’s an entry in a new record: cash in, amount, date. From there, everything you spend in that currency is tracked in its own ledger. At any point you can look at that record and know exactly how much you have left — without conversion, without estimation.
Recording in the moment
The window for recording a transaction is short. Once you’ve paid and moved on, you’ll forget the exact amount. A few hours later you might remember roughly what you spent on lunch. By the end of the day it’s gone.
This means the recording has to be fast enough to do at the point of transaction — or immediately after, before you’ve left the shop or market. If it takes more than a few seconds, you won’t do it consistently. And a tracking system you use for three days before giving up is worse than not starting, because you’ll have partial records that give you a false sense of confidence.
The three things worth capturing for each transaction are the amount, a brief category (food, transport, accommodation, activities, shopping), and a short note if it’s not obvious. That’s enough to be useful later. Anything more becomes a burden.
The offline requirement
Travel is one of the clearest cases for offline-first software. Airports, trains, rural areas, international data plans that don’t cover everywhere — the assumption that you’ll always have a reliable internet connection when you want to record something is wrong often enough to break any system that depends on it.
An app that requires the internet to function — to save a transaction, to load your balance, to do anything — will fail you at exactly the moments you need it. The solution is an app that stores everything locally on your device and doesn’t need a connection for any of its core functions.
Backup and sync are different questions. Having your records safely backed up is genuinely useful — if you lose your phone, you lose your records. But backup can happen when you’re connected, as a background process. It shouldn’t be a prerequisite for recording a transaction.
At the end of the trip
With a separate record for each currency, the end-of-trip review is straightforward. You can see what you spent in each country, broken down by category. You can see whether your estimates were accurate, where you overspent relative to expectations, and what that particular trip actually cost.
That information is worth having — not to feel guilty about spending money on holiday, but because it makes the next trip’s planning more accurate. Most people consistently underestimate certain categories (food, typically) and overestimate others. Knowing your own patterns is more useful than any generic “how much to budget for a week in X” article.
The goal isn’t perfect accounting. It’s enough of a record to stay oriented while you’re travelling, and enough to understand what happened afterward.