Most budgets die in the third month. Not because people lack willpower, but because a forty-line spreadsheet has to be kept up, and nobody keeps up forty lines.
What survives fits in three figures.
Why spreadsheets fail
A detailed budget asks two things at once: record every spend, and classify every spend. The first is a habit, the second is a decision. Multiply by forty lines and thirty days and you get twelve hundred micro-decisions a month.
Nobody keeps that up, and it is not a character flaw. A system that costs more energy than it saves stops, always, and usually around week nine.
The way out is not more discipline. It is shrinking the system until it holds on its own.
What comes in
Your salary, and everything that arrives regularly. One figure. If it varies, take the lowest of the last three months: a budget built on a good month breaks in the first ordinary one.
Count what actually lands in the account, after tax if you are on France’s pay-as-you-earn system. Bonuses and thirteenth months do not go here: they are exceptional, and letting them into the reference figure makes every other month feel disappointing.
Time: two minutes.
What leaves without asking
Rent, insurance, subscriptions, loans. Everything that goes on its own, every month. Write them down once with their day. It is the longest part, and you will not do it again.
Open your last three statements rather than working from memory. You will find two or three forgotten lines, and above all you will have the right dates, which matter as much as the amounts.
Add annual charges divided by twelve. Property tax, insurance paid in one go, the car service, a quarterly health top-up. This is the step everyone skips, and the one that makes a budget that looks right miss by a hundred euros a month.
Time: fifteen minutes, once.
What remains
The subtraction. That is your money left to live on, and it is the only figure to watch afterwards.
Divide it by the days remaining and you get a daily landmark. It is not a limit to respect to the cent, it is a scale: knowing you are on 33 € a day makes a 45 € restaurant instantly readable.
Time: three minutes.
What you do not do
You do not categorise. Not the first time. Categories tell you where the money goes, which is interesting but prevents no spending. They can come in the second month if you feel like it.
You do not reconstruct the past. Rebuilding three months of spending takes an evening and teaches you nothing your statements do not already say. The budget starts today.
You do not set a savings target. A target set before you know your real figure is an invented number. Live one month with the true figure first.
The twenty minutes, minute by minute
0 to 2 what comes in, lowest of the last three months
2 to 17 fixed charges, statements in hand, with their day
plus annual charges divided by twelve
17 to 20 the subtraction, divided by the days remainingBy the twentieth minute you have a figure you did not know and that will not change much. That is the whole point: what is long is not repeated, what is repeated is short.
What it becomes after three months
The first month is for seeing. The figure looks low, and that is normal: you are seeing for the first time what was already true.
The second month, you spot the two or three lines that cost without serving. That is where savings happen, not in giving up coffees.
By the third, the figure has become a reflex. You no longer make a budget: you know where you stand, which is not the same thing and takes ten times less energy.