Which Debt Should You Pay Off First? The Cash Flow Index, Explained

If the month is tight, rank your debts by their Cash Flow Index and start with the lowest. The index is each debt's balance divided by its minimum monthly payment. A low number means a debt takes a lot out of every month for a relatively small balance, so clearing it frees the most monthly cash for each dollar you put toward it.

If you already have real room at the end of each month, the math shifts. Paying the highest interest rate first will usually cost less in total interest. So the honest answer depends on which you're short on: monthly breathing room or total cost.

This is a cash-flow ranking method, not a universal payoff rule. Keep required payments current on every account; check loan terms, promotional deadlines, fees and any applicable borrower protections before changing your plan.

Why the interest rate feels like the whole answer

We're trained to watch one number. When rates move half a percent, whole markets react. So it feels natural to assume the highest rate is the most dangerous debt.

But a rate only tells you what a debt costs to keep. It doesn't tell you how much of your month it takes.

Every debt has three moving parts: the rate, the balance, and the term. Together they set the monthly payment, and the payment is what you actually live with.

Think about how debt gets sold. At a car dealership, one of the first questions is what monthly payment you want to stay around. The monthly payment is the number that decides what feels affordable. The Cash Flow Index uses the same number to decide what to pay off first.

The Cash Flow Index

The Cash Flow Index is a calculation popularized by Garrett Gunderson. Divide a debt's balance by its minimum monthly payment. That's the whole formula.

By that ranking, the personal loan at 20 comes first, the card at 50 sits right on the line, and the student loan at 122 comes last. Paying the student loan down first would free the least cash flow for every dollar put toward it.

Notice what the ranking ignores: the interest rate. That's deliberate. The index measures how hard a debt pulls on your month, and nothing else.

A worked comparison

Illustrative example.

Take two debts.

Generated images illustrate the example, not actual borrowers or their property.

A $22,000 car loan over five years at 3%. The payment is about $395 a month.

A $65,000 student loan over ten years at 6%. The payment is about $722 a month.

The instinct says attack the student loan. It has twice the rate and nearly twice the payment.

Run the index. The car loan: $22,000 divided by $395 is about 55.7. The student loan: $65,000 divided by $722 is about 90. The car loan ranks first.

Here's why that matters in practice. Clearing the student loan takes $65,000 before a single dollar of monthly payment comes back. Clearing the car loan takes $22,000, about a third of that, and returns nearly $400 a month.

That $400 then goes straight at the student loan, every month.

The approximately $395 monthly payment is freed only after full payoff in this example. It is redirected cash, not new income. Partial payments do not necessarily reduce a fixed required payment; actual payoff amounts and loan terms vary.

When cash flow is the whole problem

Here's the situation the method was built for.

An anonymized situation, published on our workbook page. A former federal employee, taking home $5,000 a month, with around $300,000 of debt spread across 22 separate accounts. After every minimum payment cleared, $4.10 was left.

Four dollars.

Advice to attack the highest rate assumes there's something to attack with. At four dollars of margin, there isn't.

That's a structure problem. More discipline won't fix a structure that leaves four dollars. Recovering a monthly payment will, because every payment that comes back is money that can go at the next debt.

The tradeoff, stated plainly

The Cash Flow Index won't always produce the cheapest result.

If you already have several hundred dollars a month of room after your minimums, ranking by interest rate will usually cost less in total. The index accepts some extra interest in exchange for breathing room sooner.

It can also look counterintuitive. A promotional balance at 0% with a high monthly payment can carry a low index. A spreadsheet would say never pay a 0% balance early. Clearing it can still make sense when the monthly payment is what's holding everything else back.

So the order we use is cash flow first, then interest. Win back the monthly room, then turn the freed-up cash toward the debts that cost the most to carry.

The best plan is the one that still works in a hard month.

For a separate explanation of interest-first and smallest-balance-first approaches, see the Consumer Financial Protection Bureau's guide to reducing debt. That guide does not endorse the Cash Flow Index.

Put it on paper

None of this works in your head. It takes one page.

List every debt. For each one, write the balance, the interest rate, the minimum monthly payment, and one more column: balance divided by payment. Then rank them from lowest index to highest.

The ranking can surprise you. The largest balance may not be the one taking your month, and a debt that looked minor can turn out to be doing the most damage to your cash flow.

Your next step

The free Debt Clarity Workbook walks through exactly this. Every debt in one view, with the Cash Flow Index calculated for each one. It takes about 30 minutes.

Get Your Debt Clarity Workbook

For the full walkthrough, watch Episode 5 on the Avondale Crest YouTube channel.

For related decisions, explore whether to save or pay off debt first, how to assign extra income before it disappears, and planning around irregular income.

Illustrative examples throughout. Figures are for illustration and are not predictions of individual results. Educational content only. This does not constitute financial, tax, investment, legal, or licensed financial planning advice. No outcome is guaranteed.