Mathematically optimal: directing every spare euro at the highest-rate debt first, while paying minimums on everything else, minimizes total interest paid across all debts combined. Once a debt is paid off, its minimum payment rolls into the extra payment for whatever's targeted next, so the total amount you're paying each month never changes — only where it's going does.

🇵🇹 It's common in Portugal to be juggling very different rates at once: a home loan might sit at just a few percent, a personal or car loan somewhat higher, and a credit card or bank overdraft easily above 15–20%. Avalanche pushes every extra euro at that most expensive debt first.