How the calculator builds your payoff plan
Each month the calculator does five things, in order:
- Adds interest to every debt at its monthly rate (APR ÷ 12).
- Applies each debt's minimum payment toward that debt.
- Picks the target debt — highest APR for avalanche, smallest balance for snowball — and applies the extra payment to it.
- When a debt is paid off, its minimum payment is freed up and rolled onto the next target. This is what makes the extra payment grow over time, even if you never increase it yourself.
- Records the total balance for the month so the chart and "interest saved" comparison can be drawn.
Avalanche vs. snowball: which to choose
Both methods use the same core mechanic — make minimum payments on every debt, then direct any extra money toward one target debt at a time, rolling each freed-up payment onto the next target as debts are eliminated. The difference is which debt you pick first.
| Method | Targets first | Best for |
|---|---|---|
| Avalanche | Highest interest rate | Minimizing total interest paid |
| Snowball | Smallest balance | Motivation and quick visible wins |
Avalanche is mathematically optimal — it always pays the least total interest. Snowball typically costs more, but research has shown people who watch individual debts disappear faster are more likely to stick with the plan. The right method is the one you'll actually finish.
What "minimum payment" means in this calculator
For each debt you enter a minimum monthly payment as a fixed dollar amount. This calculator holds it constant for the life of the debt. Real credit-card minimums are usually a percentage of the balance (1–3%) plus interest, and they fall as the balance falls — which extends payoff in practice. If you want a pessimistic estimate, leave the minimum at its current level; if you want an optimistic one, adjust it down as the balance shrinks. Either way, the comparison between strategies stays valid.
How interest is estimated
Interest accrues monthly at the APR you enter divided by 12. It is added to the balance before the payment is applied (the convention used by virtually all credit-card issuers and unsecured installment lenders). Promotional rates, deferred-interest offers, and minimum-finance-charge fees are not modeled.
Limitations of the model
- Doesn't model variable rates, intro APRs, balance-transfer offers, or deferred-interest "no interest if paid in full" promotions.
- Treats minimum payments as fixed; in reality most credit-card minimums step down as the balance falls.
- Excludes late fees, over-limit fees, returned-payment fees, and annual fees.
- Assumes you continue making the extra payment every month without interruption.
- Ignores tax effects (some debt interest, like mortgage interest, may be deductible — credit-card interest is not).
The power of extra payments
On high-interest credit card debt, the minimum payment barely covers the monthly interest — your balance barely moves. Here's what happens to a single $5,000 credit card balance at 22% APR with a $100/month minimum, depending on whether you add an extra payment on top:
| Plan | Months to payoff | Total interest | Interest saved |
|---|---|---|---|
| Minimum only ($100/mo) | 137 months (≈ 11.4 yrs) | $8,678 | — |
| +$50 extra ($150/mo) | 52 months (≈ 4.3 yrs) | $2,798 | $5,880 |
| +$100 extra ($200/mo) | 34 months (≈ 2.8 yrs) | $1,750 | $6,928 |
| +$200 extra ($300/mo) | 21 months (≈ 1.8 yrs) | $1,022 | $7,656 |
An extra $50/month — about $1.65/day — cuts payoff time from over 11 years to under 5 and saves nearly $5,900 in interest. The marginal value drops as you add more, but every extra dollar still pulls forward the payoff date.
Tips to find extra money for debt payoff
- Use windfalls: tax refunds, bonuses, and gifts applied directly to your highest-priority debt can have an outsized impact.
- Automate the extra payment: set up an automatic additional payment so it happens without willpower.
- Consider balance transfers: a 0% APR balance transfer card can temporarily eliminate interest, letting your full payment reduce principal.
- Refinance high-rate debt: a personal loan at a lower rate than your credit cards can reduce your total interest significantly.
Frequently asked questions
Should I invest while paying off debt?
It depends on the interest rate. If your debt rate is higher than what you'd expect to earn investing (roughly 7% for a diversified stock portfolio), paying off debt first is the better financial move. An exception: always contribute enough to get your full 401(k) employer match — that's an instant 50–100% return that beats any debt-payoff math.
Does paying off debt hurt my credit score?
Generally no — paying off debt improves your credit score by reducing your credit utilization ratio (balances ÷ credit limits). Closing accounts after payoff can temporarily reduce your score, so consider keeping paid-off credit cards open with a zero balance.
What if I can only afford minimums?
Pay minimums consistently to avoid late fees and credit damage. Look for any discretionary spending to cut, even temporarily. Even an extra $25/month makes a difference over time. If you're truly unable to manage, contact a nonprofit credit-counseling agency — they offer free advice and may be able to negotiate lower rates through a debt management plan.