Debt payoff strategies — avalanche, snowball, and amortization

What amortization is (and isn't)

Every standard loan — mortgage, auto, student, personal — amortizes. That means each monthly payment is split between interest (paid first) and principal (the rest), with the split shifting toward principal over time as the balance shrinks.

A 30-year mortgage at $400,000 and 6.5% has a monthly payment of about $2,528. In month one, ~$2,167 of that is interest and only ~$361 reduces the principal. By year 25, that ratio inverts. Same payment; different work it does.

Amortization isn't a "strategy." It's how the loan is structured by default. The strategy question is: do you make extra payments? And if so, which loan first?

Avalanche — the math-optimal strategy

Pay the minimum on every debt, then throw any extra dollars at the debt with the highest interest rate.

Why it works: every dollar you put against your highest-rate debt saves you that rate, every year, until the debt is gone. A 24% credit card balance compounds against you faster than an 8% student loan or a 6.5% mortgage. Killing the credit card first saves the most total interest.

Example: $20,000 across three debts.

• Credit card: $5,000 @ 24%
• Student loan: $10,000 @ 6.5%
• Auto loan: $5,000 @ 8%

You can pay an extra $500/mo. Avalanche order:

1. Credit card first (24% rate)
2. Auto loan next (8%)
3. Student loan last (6.5%)

Total interest paid: roughly $1,800. Total time to debt-free: ~38 months.

Snowball — the behavior-optimal strategy

Pay the minimum on every debt, then throw any extra dollars at the debt with the smallest balance.

The case: paying off a small debt completely is a win you can feel — fewer monthly bills, simpler statement, dopamine hit. Behavioral economists (Dave Ramsey is the loudest advocate) argue that people stick with debt-payoff plans longer when they get visible wins early, even if the math is slightly worse.

Same example. Snowball order:

1. Credit card ($5,000 — smallest)
2. Auto loan ($5,000 — tied; usually pick by interest)
3. Student loan ($10,000 — largest)

Wait, in this example avalanche and snowball pick the same first debt — credit card. That's common because the smallest debt is often also the highest-rate (credit cards). Snowball usually only diverges from avalanche when you have a small low-rate debt and a big high-rate debt.

Example where they diverge: $1,500 credit card @ 18% and $20,000 student loan @ 24%.

• Avalanche: student loan first (24% > 18%).
• Snowball: credit card first ($1,500 < $20,000).

Snowball costs about $200–$400 more in total interest in this scenario. Whether that's worth it depends on whether you'd actually finish.

When to pick which

Pick avalanche if:

• You're disciplined enough to keep paying the same monthly amount even when no debt looks dramatically different month-to-month
• You have a spreadsheet and you check it
• The interest-rate spread between your debts is large (>5 percentage points)
• The difference in total interest is meaningful to you in absolute dollars

Pick snowball if:

• You've started and abandoned debt-payoff plans before
• You have multiple small debts that feel overwhelming as a list (credit cards spread across cards)
• You need a visible win in the first 6 months to stay motivated
• The total interest difference is small in absolute dollars

For most households with conventional debts, the total interest difference between avalanche and snowball is a few hundred dollars over a decade — small in absolute terms, even if the percentage difference looks scary. Your actual completion rate matters more than your theoretical interest savings.

What about the mortgage?

Mortgage interest rates are usually the lowest of any consumer debt (in 2024–2026, often 6–7%), and mortgage interest may be partially deductible if you itemize. Most personal-finance frameworks suggest:

1. Pay off all credit cards (rates often >15%)
2. Pay off auto loans / personal loans (rates often 7–12%)
3. Pay off student loans (rates often 4–8%)
4. Decide whether to accelerate the mortgage (rate often 6–7%)

That last one is genuinely a judgment call. The math says: if your expected investment return after tax exceeds your mortgage rate, you're financially better off investing the extra money. If you're risk-averse, the guaranteed return of paying down the mortgage may feel better than the expected return of investing.

A trap: minimum-payment treadmill

Both avalanche and snowball assume you're making the minimum payment on every other debt while attacking the priority one. If you skip a minimum, the strategy fails — you pile up late fees, your credit takes a hit, and the math collapses.

Set up auto-pay for the minimums on every debt. Then your "strategy" is just: where does the extra discretionary income go each month?

How Horizons models this

In your Liabilities page, every debt has an interest rate and a linked payment expense. The forecast engine pays the minimum on each loan and routes any surplus per your BudgetRules debt_payoff_strategy setting:

• avalanche — surplus goes to highest-rate debt first
• snowball — surplus goes to smallest-balance debt first

Switch between them in the budget-rules UI and re-run your forecast to see the difference in total interest paid and net-worth trajectory. Most users find the two strategies produce very similar net-worth lines after 10 years.

A quick gut-check

Forget the math for a moment. Ask yourself: if I picked one strategy, would I actually stick with it for the next 4–7 years? If the answer is "snowball is the only way I'll finish," then snowball is the better strategy for you, even if it costs a few hundred extra dollars in interest. The strategy that gets you to debt-free wins, regardless of which spreadsheet says it's optimal.

Check your understanding