Budgeting in euros: what actually differs

Most budgeting method is written for a currency and a calendar that are not yours. It usually still works — the ideas are not about the euro — but four things genuinely differ, and every one of them changes what the software has to do.

One salary, thirty days

In most of Europe, pay arrives once a month. In France it is the norm rather than a choice. That single fact reshapes the problem: you receive one amount and have to make it span a period during which nothing else arrives.

The frequency is not neutral. De La Rosa and Tully studied it directly, across field data from 30,828 consumers and five experiments, and found that higher payment frequency leads to more spending — people paid daily rather than weekly spent about $20 more per month. The mechanism they identify is not impulsiveness: more frequent pay reduces uncertainty about having enough to get through the period, which raises how wealthy people feel, which raises what they spend.

Turn that around for a monthly salary and you get the European condition exactly. One inflow, maximum distance to the next one, maximum uncertainty about whether it will stretch. That is not a character trait. It is a harder arithmetic problem, and it is the one the whole month is spent solving.

The detail that matters most is in their fourth study: the effect disappeared when the timing of expenses matched the timing of pay. The problem was never the frequency itself. It was the mismatch between when money arrives and when it leaves.

Which is a fair description of what an envelope budget does. It cannot make your salary arrive weekly. It can make one arrival on the 1st into a set of amounts that each have a date and a job — closing the mismatch on the side you can actually control.

A third of it is already committed

Before you decide anything, a large part of the month is spoken for.

INSEE measures this as dépenses pré-engagées — spending “assumed to take place under a contract that is hard to renegotiate in the short term”: housing, water, gas, electricity, telecoms, insurance, financial services. In 2024 it came to 30.3% of households’ gross disposable income, of which housing alone was 22.8%.

One caveat, and it is a real one: that figure is a national-accounts measure and includes imputed rents — the theoretical rent owner-occupiers would pay themselves. It is not a claim that 30% of your bank account leaves by direct debit. What it does establish is the shape: a large, stable, contractual block of the month that is decided long before the month starts.

For a budget, that block is not a problem to solve. It is a set of dates. Rent on the 3rd, the loan on the 8th, insurance on the 12th, energy on the 20th. Each is known, each is automatic, and the only useful question about them is whether the money will be there on the day.

That is why scheduled payments carry a date and not just a monthly amount, and why an envelope that will not cover its next dated payment says so: €40 short by 15 March. The commitments are not the interesting part of your budget. They just have to stop being a surprise.

The comma is a decimal separator

1 234,56 €. Not €1,234.56.

This looks like cosmetics and is not. It is the single most common reason a CSV import produces silently wrong numbers rather than an error — parse 1.234,56 with a dot-decimal assumption and you get 1.234, a thousandfold error that looks like a plausible amount. The file imports. The totals are nonsense.

Two places this has to be handled, and they are different problems.

Reading, where the same string has two meanings depending on where the file came from. This is dealt with in the import guide, because it is the moment it bites.

Writing, where amounts are typed by hand. A field that only accepts a dot forces people to type against their own keyboard and their own habits. Arca accepts the comma and normalises it, and displays money through the locale rather than a hard-coded format — so a French budget shows 1 234,56 € and an English one €1,234.56, from the same stored value. Money is held in cents, as integers, which is what keeps a sum of amounts from drifting the way decimals do.

Currency belongs to the account, not to you

The design decision here is worth stating plainly, because most tools make the opposite one.

Arca does not have a “budget currency” setting. Each account carries its own currency, and the budget’s currency is derived from the accounts inside it — the oldest one wins. You never convert an account from euros to pounds; you open a second account and transfer between them, which is what actually happened.

The consequence is the honest part. An account in another currency is tracked, not budgeted: it appears in your net worth, and it is deliberately excluded from the envelopes. Exchange rates are stored as dated records, so a past month keeps the rate it was converted at rather than being silently rewritten by today’s.

That is a real limitation and it is chosen. Letting a dollar account feed euro envelopes would mean every envelope balance moved when the rate moved — and an envelope whose balance changes because a currency market moved is no longer telling you what you can spend.

If your income and your spending are in two currencies, that is a genuinely harder problem than this handles today.

What this does not do

The same honesty as everywhere else in these guides:

No bank connection. Manual entry or CSV import. It is a choice: plugging an aggregator into your account grants it standing permission to read, and that surface does not come à la carte. The reasoning is in this guide.
No native app. It is a web application. It works on a phone, but it is not installed from a store.
No shared household budget. Not available.
No published price. Arca is in free public beta. It will become paid, with at least 60 days’ notice by email and the exact figure — and nothing charged without an explicit order from you. We would rather publish no number than one we might not hold.

None of this is about the euro being special. It is that a method arrives with assumptions baked in — how often you are paid, which character separates the units from the cents, whether the balance you see is one currency or several — and the assumptions are the part that does not travel. The method travels fine. It is the defaults that need translating.