The 50/30/20 rule is the gentlest way into budgeting: roughly 50% of your take-home on needs, 30% on wants, 20% on savings and debt. It's popular because it's forgiving — no tracking every coffee, just three buckets and a rough split. Purists will tell you it's too loose, and for tight budgets they've got a point (sometimes needs alone blow past 50%). But as a starting frame, it's hard to beat.
This tool works out your 50/30/20 split from your income and then lets you check reality against it — because the rule is easy to state and surprisingly easy to drift from. Just put your numbers in and see how your actual spending lines up. No signup, no bank login.