In zero-based budgeting, you assign every euro of monthly income to a category — spending, saving or debt repayment — until the remaining balance is zero. No money is left “unassigned”.
Versus the 50/30/20 rule, which distributes by percentages, this method forces intent on every euro. It works particularly well if you keep ending months short without knowing why.
It requires a review at the start of each month and a mid-month adjustment if anything unexpected hits. An app that logs spending in the moment makes the control much easier. A spreadsheet works too, but is heavier to maintain.