The Debt You Cannot Out-Earn

Paying a debt is a guaranteed return

A debt has a rate on it, and clearing the balance stops that rate. So the money you use to clear it earns exactly that rate, with no market risk and no forecasting: it is the closest thing in personal finance to a risk-free return, and it is why the comparison is not “debt versus investing” but *two rates* — one contractual, one expected. That reframing makes the decision mechanical. A card at 22.9% is a guaranteed 22.9% on every dollar applied to it. An equity portfolio is an expected 7% with a distribution that includes years of −20% or worse. Ranking a certain number against an uncertain one at half the size is not a hard problem, and it does not require an opinion about the market at all — which is the point, because the household does not have to be right about anything to come out ahead. It also explains why “the minimum is fine if I pay on time” is so expensive. A minimum payment is designed to keep the account current, not to clear the balance: on a $12,000 balance at 22.9%, the first month’s interest alone is about $229, so a $180 minimum does not even cover the interest and the balance grows. Time-on-the-books is the lender’s product, and only a payment above the interest line shortens it. The same balance, two payments — Balance, rate: $12,000 at 22.9% (1.908% a month) · Interest in the first month: $229 · Payment of $180 — the minimum: below the interest line: the balance grows · Payment of $500: clears in ≈ 32.4 months, ≈ $4,200 of interest · Payment of $750: clears in ≈ 19.3 months, ≈ $2,456 of interest ← Paying $250 more a month saves about $1,744 and more than a year — the extra money attacks interest that has not been accrued yet, which is why the payoff time is not linear in the payment.

Where the debt sits in the order

Spare cash has several possible destinations and they are not equal, so the plan needs an order. First, the employer match: a 50% or 100% match is an instantaneous return no market offers, and it is usually available only through the workplace account. Second, high-interest debt — roughly anything in double digits, and certainly cards, payday loans and buy-now-pay-later balances in their deferred-fee form. Third, a starter buffer, and then the full three to six months (PF3). Fourth, tax-advantaged investing, and finally a taxable account. The ordering has one genuinely debatable joint: the starter buffer against the debt. The reason to build one month of essentials first is that a household paying every spare dollar at a card is one flat tyre away from re-borrowing — and a re-borrowed balance is usually larger than the payment that would have prevented it. The reason to attack the debt first is the rate. Both arguments are sound, which is why most plans do a small buffer first and then concentrate on the debt. Low-rate debt is a separate case, and treating it as an emergency is a mistake in the other direction. A mortgage at 3% or a subsidised student loan at 4% is cheaper than the expected return on a diversified portfolio, so paying it down early is a choice between two reasonable uses of money rather than an obvious win. The honest comparison is after-tax and risk-adjusted: mortgage interest may be deductible, the debt is fixed while the portfolio is not, and equity risk is real. Pay it down if the certainty is worth more to you than the expected spread; invest if the horizon is long and the payment is comfortable. The order spare cash travels in — 1. Employer match: an instant 50–100% — no market offers this · 2. High-interest debt: a guaranteed 15–25% on every dollar applied · 3. Starter buffer, then the full buffer: so a shock is not funded by new debt · 4. Tax-advantaged investing: then taxable ← Two things to avoid with old debt. Do not close the oldest card to “clean up” — length of credit history is part of a score, so keep it open with a small recurring charge. And treat consolidation carefully: moving a balance to a lower rate helps only if the old card is not refilled, because the behaviour is what created the balance.

The method you finish beats the method that is optimal

Two systems compete for repayment order. The avalanche targets the highest rate first and is unambiguously cheaper in total interest. The snowball targets the smallest balance first, which clears an account faster and produces visible progress — and in the randomised studies and practitioner data on repayment, the ordering people actually complete is the one that reduces the balance. That is not an argument for abandoning arithmetic; it is an argument for knowing which kind of problem you have. If the household has one card and a clear surplus, the avalanche is strictly better and costs nothing to follow. If it has six accounts and a history of starting repayment plans and abandoning them, the difference in total interest between the two orders is usually small enough that finishing matters more than the ordering. One thing both systems share is a floor. A household should keep paying at least the minimum on every account at all times, because a missed payment damages a credit report for years and can raise the rate on every other balance — turning a cash-flow problem into a price problem. Payroll-deducted automation does more for a repayment plan than any amount of resolve. Two orders, one list — Balances: $6,000 at 24% · $2,500 at 19% · $900 at 0% (promo) · Avalanche: 24% first — cheapest in total interest · Snowball: $900 first — fastest visible win ← · Both: minimums everywhere, every month, automated A promotional 0% balance is a real trap of a different sort: when the promo ends, the rate often resets retroactively high, so the useful question is what the balance will look like on the day it expires.

The debts differ, and one of them is dangerous

The interest rate orders the debts, and the rate is not the only property that matters. Two debts at the same rate can have completely different risk characteristics, and treating them as interchangeable because the arithmetic matches is how a household ends up optimising the wrong thing. The first distinction is **secured against unsecured**. A mortgage or a car loan is secured by an asset the lender can take; failing on it costs the asset and damages credit but does not usually chase the borrower further, because the lender’s remedy is the collateral. An unsecured card balance or personal loan has no collateral, so the lender’s remedy is the legal system and the borrower’s income. The practical consequence is that a secured debt in trouble is a problem about a house or a car, while an unsecured debt in trouble is a problem about cash flow and legal exposure — different failures, different responses. The second is **recourse and the option embedded in the loan**. A fixed-rate mortgage is not merely a debt; it is a debt plus an option to refinance if rates fall, which belongs to the borrower and is worth something. That option is why a fixed-rate mortgage at a low rate is an asset worth keeping even when the same money could repay it, and why the decision to prepay should consider the rate being given up rather than only the rate being paid. A variable-rate loan has no such option: the borrower bears the rate risk, and the same analysis runs the other way. The third is the **tax treatment**, which changes the effective rate rather than the stated one. Mortgage interest may be deductible, which lowers the true cost for households that itemise; student loan interest has its own deduction with an income phase-out; and interest on consumer debt is generally not deductible, which is one reason a card balance is the worst cost on the list. Computing the effective rather than the nominal rate is what makes the comparison with an investment honest. That comparison is the decision underneath all of them: repay or invest spare cash. Repaying a debt at a known rate is a guaranteed return, and an investment is an uncertain one, so the comparison is not simply “which rate is higher”. The useful framing is that repayment is a risk-free return equal to the after-tax rate, whereas the investment’s expected excess return over that is usually a couple of percentage points with a wide dispersion. A household with a high-rate unsecured balance and spare cash has a risk-free, tax-free option that most investments cannot beat on a risk-adjusted basis; a household with a low-rate fixed mortgage has an option to keep cheap money for decades, which is a different decision entirely. So the ordering the lesson builds should be read with these properties attached: the rate sets the urgency, and the structure sets the consequence. A cheap secured loan and an expensive card are not the same kind of problem, and the plan should say which one is the one that could actually change a household’s life. • Secured and unsecured debts fail differently: an asset versus an income stream. • A fixed-rate mortgage includes a refinancing option that belongs to the borrower. • Effective rates, not stated ones, are what compare against an investment. • Repayment is a risk-free after-tax return, which changes what it has to beat. A rule of thumb that survives the details: repay anything above a mid-single-digit after-tax rate before investing beyond a matched employer contribution, and treat a low-rate fixed mortgage as cheap long-term financing rather than as a debt to clear.

Sources

• Credit card rates and the cost of minimum paymentsConsumer Financial Protection Bureau — credit card interest and minimum-payment guidance
• Order of operations for spare cashBogleheads wiki — investment policy and prioritizing investments
• Avalanche versus snowball debt repaymentBehavioral repayment research and consumer-finance practitioner guidance
• Recourse debt, collections and the credit reportCFPB — debt collection and credit reporting guidance