Debt Avalanche With a 0% Intro APR Card: How to Run the Math
If you're using the debt avalanche method, the instructions sound simple: attack the highest interest rate first. But what happens when one or two of your credit cards are sitting at 0% for the next 12 months? A 0% rate is the lowest rate you have, so does it go last? Do you ignore it? Do you throw everything at it before the promo ends?
Brian walks through it on video.
This is one of the most common questions I get about the avalanche method, and the answer is a two-step calculation you can do on a napkin. Let's walk through it.
Quick refresher: what the avalanche method actually does
You have several debts. Each one has a balance, an interest rate, and a monthly payment. The avalanche method says: list them by interest rate, highest first. Pay the minimum on everything, and any time a debt gets paid off, take that freed-up payment and add it to the highest-rate debt still standing.
That's the whole thing. You don't send more money than you were already sending. Your total monthly payment stays the same. What changes is where the money goes once a debt disappears.
The snowball method does the same rollover trick, but orders debts by smallest balance instead of highest rate. That gives some people a faster emotional win. Apples to apples with multiple debts, though, the avalanche usually wins on total interest and total months, because the highest-rate debt is the one hitting you with a disproportionate amount of interest. If you want to compare the two side by side, use the avalanche vs. snowball tool.
Why a 0% card breaks the normal avalanche order
A 0% intro rate isn't permanent. It's a rate that applies for a set number of months — often 12 — and then a real rate takes over. So if you sort your debts by today's rate, the 0% card goes dead last and stays there. That's fine for the next 12 months. It's wrong on month 13, when that card might jump to 20-something percent and become the debt you should have been planning for all along.
The other thing to understand about 0%: during the promo, every dollar of your payment goes to principal. None of it is eaten by interest. That makes the math on those months dead simple — no amortization, no compounding, just subtraction.
The two-step fix
Here's how I'd handle it.
Step 1: Fast-forward the 0% debts to the end of the promo
Multiply the monthly payment by the number of interest-free months left. Subtract that from the balance. What's left is the balance you'll be carrying when the promo ends.
Step 2: Start your avalanche plan from that point
Enter those fast-forwarded balances — along with the interest rate that kicks in after the promo — into an avalanche calculator, together with your other debts. Now you're planning for the real fight instead of a temporary rate.
A worked example with simple numbers
Say you have two cards, both at 0% for 12 more months:
| Debt | Balance today | Monthly payment | 12 months of payments | Balance at month 12 |
|---|---|---|---|---|
| Card One | $10,000 | $300 | $3,600 | $6,400 |
| Card Two | $6,000 | $200 | $2,400 | $3,600 |
$300 × 12 = $3,600, so $10,000 − $3,600 = $6,400 left. $200 × 12 = $2,400, so $6,000 − $2,400 = $3,600 left. Two multiplications, two subtractions, done.
Now you build your avalanche plan using $6,400 and $3,600 as the starting balances, at whatever rates those cards revert to, alongside your other debts. Run it in the debt avalanche calculator and you'll see your payoff order, your payoff date, and your total interest.
What the avalanche saves when you run it properly
Here's a three-debt example that shows the size of the effect. A credit card with $10,000 owed at 24% and a $300 payment. A personal loan of $14,000 at 11% with an $800 payment. A car loan taking $450 a month. Total balances $31,000, total payments $1,550 a month.
Pay each debt on its own separate schedule and you're looking at $7,117 in interest, with the longest debt taking 52 months. Run the exact same balances and the exact same $1,550 a month through the avalanche — rolling each freed-up payment onto the highest rate — and interest drops to about $5,000. That's $2,151 saved, and the whole thing is finished in 24 months instead of 52. You cut 28 months off, over two years, without sending a single extra dollar.
Where the money moves
In month one you send $300, $800 and $450, just like before. When the car loan finishes, that $450 does not go to the 11% personal loan — it goes to the 24% card, making that payment $750. When the personal loan finishes, its $800 goes to the same place. That's the avalanche in action.
The trap to watch: minimums that don't cover interest
One more thing worth checking while you're in the calculator. Take that $10,000 card at 24%. At $300 a month it takes 52 payments and costs $5,458 in interest. But if the card company tells you the minimum is $100 and you pay $100, the calculator gives you a very different answer: payment too low to cover interest. That debt is never paid off. Ever.
So just because a lender says you "only have to pay" a number doesn't mean that number gets you anywhere. Test it. If the calculator can't produce a payoff date, raise the payment until it can. The credit card payoff calculator will show you the same thing on a single card.
What about extra money each month?
If you find an extra $100 in your budget, you don't have to guess which debt gets it. Add it to the extra payment line and the avalanche answer is always the same: it goes to the highest rate. In the example above, the 24% card's $300 payment simply becomes $400, and your payoff date moves up.
There's a flip side worth being honest about. When a debt gets paid off, you could take that freed-up $450 and do something else with it — park it in savings, invest it. Sometimes it's worth looking at opportunity cost. I've written about that math in savings account vs. paying off debt. But when the highest rate on your list is in the twenties, the debt usually wins.
A short checklist
- Write down every debt: balance, rate, minimum payment.
- Note which debts are at 0% and how many promo months are left.
- For each 0% debt: payment × months left, subtracted from the balance.
- Note the rate that applies after the promo ends.
- Enter the fast-forwarded balances and post-promo rates into the calculator with your other debts.
- Make sure no payment is too low to cover interest.
- Keep the total monthly payment constant and roll every freed-up payment to the highest rate.
Bottom line
A 0% intro period is a gift, but it's a gift with an expiration date. Use those interest-free months to knock down principal fast, and plan your avalanche around the balance you'll actually be holding when the clock runs out — not the zero on your statement today. The math takes about a minute, and the payoff is measured in years.
Run your own numbers in the Avalanche Debt Eliminator, and if you're still deciding between methods, start with building a payoff plan that actually works. Nobody else is going to do this for you — the banks aren't, and the government isn't. It's up to you to take care of your financial future.