Three boxes for your paycheck

The 50/30/20 rule splits your paycheck into three boxes: half for needs (housing, food, utilities), thirty percent for wants and life, and twenty for saving and paying off debt. Elizabeth Warren popularized it alongside her daughter in the book "All Your Worth."

With 1,500 € net: 750 € to live on, 450 € to enjoy, 300 € for your future. If your rent breaks the first box —common in big cities—, you don't throw the rule out: you adjust by trimming the thirty box, not the twenty.

Its value isn't in the precision but in the map: it forces saving to have a reserved percentage instead of being the leftover balance at month's end. An imperfect budget you actually keep always beats a perfect one that doesn't exist.