The snowball pays the smallest balance first
You keep paying every minimum, then put every spare dollar on the debt with the smallest balance. When it clears, its payment joins the pile and moves to the next smallest one. Balances disappear quickly early on, and that is the point: the plan you keep doing beats the plan that looks best on paper.
The avalanche pays the highest rate first
Same rolling payment, different target: whatever charges the most interest goes first, however much it owes. That always costs the same or less than the snowball, and usually finishes at least as soon. The catch is patience — a big, expensive loan can sit at the top of the list for a year before anything gets crossed off.
The gap between them is usually smaller than the extra
Run both above with your own numbers. On most real debt loads the difference between the two orders is a few hundred dollars, while another $100 a month is worth thousands. Pick the order you will actually stick to, and spend the argument on finding the extra instead.
What a minimum payment actually does
A credit card minimum is usually about 1% of the balance plus that month's interest, with a floor near $25 — and it falls every month as the balance does. That is the trap: the payment shrinks as fast as the debt, so a $6,000 card at 24.99% APR starts around $185 a month and is still going more than twenty years later, having cost more in interest than the balance you began with. A loan is the opposite. Its payment is fixed, so the same amount buys more principal every month and the end date is set from the start. This page treats the two differently for exactly that reason: it asks a loan what you pay, and works a card's minimum out for you, month by month, the way your issuer will. Anything above the minimum goes straight at the principal, and it compounds — it lowers next month's interest, which lowers the month after that. That is the whole trick, and it is why this page asks for the extra before it asks for anything else.
When a payment can't cover its own interest
If what you pay is less than the interest a debt charges that month, the balance goes up, not down. This calculator says so, per debt, instead of quietly projecting a payoff date that will never arrive.
Promotional rates and deferred interest
A 0% promotional rate is not modelled on this page: enter the rate you'll pay when it ends, and treat the date as optimistic until then. Inside the app, a debt can carry a promotional APR with an end date, and the plan switches to the regular rate on that date. Deferred interest — where the whole period's interest lands at once if you don't clear the balance — isn't the same thing as 0%, and neither this page nor the app models it.