Good Debt vs. Bad Debt on the Path to FIRE: A Framework for Every Life Stage
One of the most counterproductive things I see in the FIRE community is debt absolutism: the belief that all debt is bad and should be eliminated immediately. This thinking leads people to pay down low-rate mortgages instead of investing (see: pay off debt or invest — the math), avoid business loans that would generate far more than they cost, and treat every liability as an emergency.
I built real wealth partly through strategic use of leverage. That doesn’t mean borrowing recklessly. It means having a clear framework for which debt builds wealth and which destroys it.
The Framework: Four Questions for Any Debt
- What is the after-tax interest rate? Mortgage interest may be deductible. Business interest often is. The effective cost of money matters more than the nominal rate.
- Does this debt purchase an asset that appreciates or generates income? A rental property mortgage purchases an appreciating, cash-flowing asset. A car loan purchases a depreciating one.
- Is the payment obligation fixed or variable? Fixed-rate debt is predictable and plannable. Variable-rate debt introduces risk, especially at FIRE when income may be limited.
- What is the opportunity cost of the alternative? Paying off a 4% mortgage means forgoing ~7% expected long-term returns on index funds. The math usually favors investing. Paying off a 24% credit card is the highest guaranteed return available.
Clearly Good Debt
Fixed-rate mortgage on a primary residence (below 5%): Leverage on an appreciating asset. Tax-deductible interest. Historically, not prepaying and investing the difference has won. The psychological value of paying it down early is real, but mathematically this is wealth-building debt at the right rate.
Real estate investment loans: If the property cash-flows after mortgage payments, insurance, taxes, and maintenance, you’re using the bank’s money to acquire an asset that pays for itself and appreciates. This is classic wealth-building leverage. Underwrite carefully. Over-leveraged real estate in a downturn is dangerous.
Business financing for verified ROI: A $50,000 equipment loan that enables $200,000 in additional annual revenue has a clear positive expected value. Business debt that funds growth with a definable return profile is an investment, not a liability.
Student loans for high-ROI degrees: A nursing degree that pays $80k/year and costs $40k total in loans has a payback period under 2 years (in income above alternatives). Not all student loans are created equal — it depends entirely on the income differential the degree enables.
Clearly Bad Debt
Credit card debt carried month to month: 18–29% APR with no asset purchased. Pure consumption financing. Every month you carry a balance is a month where you’re paying $150–$240 per $10,000 borrowed for nothing except the privilege of having bought things you couldn’t afford. Eliminate first, always.
Car loans for vehicles above your means: Cars depreciate immediately and continuously. A $45,000 loan on a vehicle worth $32,000 in three years is a guaranteed wealth destroyer. Drive what you can pay cash for, or what keeps payments comfortably below 10% of monthly take-home pay.
Personal loans for lifestyle expenses: Vacation loans, wedding loans, furniture loans — all of these finance consumption with high-interest debt. None of them purchase anything that appreciates. Avoid entirely.
Buy Now Pay Later on non-essentials: BNPL products often have zero-interest promotional periods followed by 25–30% rates if unpaid. They’re designed to make consumption feel affordable while being expensive. Treat them like credit card debt.
The Gray Zone: Context Determines Quality
Student loans for lower-ROI degrees: A $90,000 MFA debt on a degree leading to $45k starting salary is mathematically challenging. Not necessarily “bad” if other life goals are satisfied, but it requires honest income expectations.
Home equity loans: Excellent rate (usually), but you’re putting your home at risk. Use for genuine investment or improvement, not for consumption or lifestyle upgrades.
Mortgages above 6%: At current rates, paying down principal has more mathematical justification than in the 3% era. Still not inherently bad — housing is a necessary expense — but the calculus on prepayment vs. investing shifts meaningfully.
The FIRE Rule: Eliminate Bad Debt Before Reaching FI
Your FIRE number assumes a sustainable withdrawal rate. Debt payments that persist in early retirement add to your required monthly withdrawal and raise your FIRE number. A $500/month car payment requires an additional $150,000 in portfolio to support at the 4% rule — a direct consequence of how the FIRE number is calculated. A $1,200/month mortgage requires $360,000 more.
Entering FIRE with good debt (a low-rate mortgage) is defensible. Entering FIRE with bad debt (consumer credit, auto loans) is a plan flaw. The clean version of FIRE: mortgage only, or debt-free entirely.