Debt payoff strategies — avalanche, snowball, and amortization

When you have multiple debts, where should extra payments go? Two strategies dominate the conversation: avalanche and snowball. Both work, both have academic defenders, and the "right" one depends more on your psychology than on the math.

The setup

Suppose you have four debts:

Minimum payments total $960/month. You have $1,200 to allocate — so $240/month of extra capacity. Where does it go?

The avalanche method

Rule: pay minimums on everything; direct all extra payments to the highest-rate debt.

With the debts above:

1. All $240 extra goes to Credit Card A (22%) until paid off.
2. Then the full Card A payment ($240 min + $240 extra = $480) rolls over to Card B (18%) on top of its $90 minimum.
3. Then the full combined amount rolls to the car loan (6%).
4. Finally the student loan (5%).

Avalanche minimizes total interest paid. In the example above, it saves several thousand dollars vs any other ordering.

The snowball method

Rule: pay minimums on everything; direct all extra payments to the smallest-balance debt.

With the same debts:

1. All $240 extra goes to Credit Card B ($3,000 balance) until paid off.
2. Then the combined $330 rolls to Card A ($8,000).
3. Then to the car loan ($15,000).
4. Finally to the student loan ($25,000).

Snowball is slightly less efficient mathematically — you're not attacking the highest-rate debt first — but delivers faster early wins. Paying off Card B in just a few months provides a psychological boost and reduces the number of debts to track.

Which one works better?

Mathematically, avalanche wins every time. The real question is behavioral: which one will you actually stick with?

Research by Northwestern's Kellogg School and others has found that snowball users have higher completion rates in debt-payoff programs. The psychological lift of eliminating a debt entirely appears to sustain motivation better than the abstract savings of attacking a higher-rate debt with a larger balance.

If the rates don't differ by much (say, a 22% credit card vs a 19% credit card), the mathematical difference is small and snowball is defensible. If the rate gap is large (22% credit card vs 5% student loan), avalanche is worth the discipline.

Hybrid approaches

Many people land on hybrids:

"Avalanche with exceptions." Follow avalanche rules except for any debt under $500, which you knock out first for simplicity.

"Snowball with caps." Follow snowball but skip any debt with a rate under 6% — pay only minimums on those and focus extra on higher-rate debts.

"Emotional avalanche." Follow avalanche, but pay off any single annoying debt (an ex's credit card, a medical bill in collections) first regardless of rate.

All of these are fine if they keep you moving forward.

The "never-negotiate" debts

Some debts should be paid fully and on time regardless of strategy:

• Tax debt — the IRS and state tax authorities have collection powers that outweigh the interest rate. Prioritize these.
• Child support or alimony — legally enforced; non-payment has consequences that dwarf any interest rate calculation.
• Any debt near default — falling behind on a single debt long enough to trigger default has credit consequences that take years to repair, often outweighing the interest saved by prioritizing other debts.

When to pay minimums only

Not every debt needs aggressive payoff. If a debt's rate is below your expected investment return, paying only the minimum and investing the difference is often mathematically superior. The break-even rate is roughly:

• If your debt rate is < 4–5%: consider investing the extra.
• If your debt rate is 5–7%: depends on risk tolerance and horizon.
• If your debt rate is > 7–8%: pay it down first.

This analysis is covered in "When to Pay Down vs Invest."

How Horizons uses this

Your Budget Rules page lets you set a debt-payoff strategy: snowball, avalanche, or a priority order you define. When your forecast shows a monthly surplus, the engine allocates extra payments according to your rule. As debts pay off, their linked expenses disappear and that cash flow can be redirected to savings or investments per the rest of your budget rules.