Car Total Cost of Ownership Priced in FI Months

The 2015 SUV in your driveway just handed you a $3,800 repair estimate, and the shiny replacement in the showroom window is whispering that this is finally the year. Most people resolve that tension on vibes. The fix is to run the car total cost of ownership on all three paths, keep the old car, swap into a used replacement, or buy new, and then translate the gap into the only unit a FIRE spreadsheet respects: months added to the FI date.

Run the full math and a pattern emerges in most scenarios. The paid-off car stays cheapest until its expected annual repair and downtime costs climb above the replacement's annual depreciation, insurance, and financing differential. Every dollar of that differential is a dollar pulled out of the market, so this is a compounding problem wearing a car costume. Below is the whole calculation, with numbers you can replace with your own tonight.

Your Car Is the Second-Biggest Line in the FI Budget

Transportation sits second only to housing in the average US household budget, consuming roughly one dollar in six, and BLS Consumer Expenditure data show housing and transportation together absorbing about half of average spending in 2024. For a FIRE accumulator that ranking carries extra weight, because FI is won and lost on the big three lines: housing, transport, food.

Scale explains why this single decision outranks a year of frugality projects. Cutting $150 a month of subscriptions and coffee frees $1,800 a year. The annual gap between keeping a paid-off car and buying new, as the table below shows, can run past $7,000, roughly four times those savings. One signature at a dealership moves more money than twelve months of small-cut discipline, and you only have to get it right once a decade.

The Full Cost Stack Behind Keep, Used, and New

The car total cost of ownership stack has seven layers, and they rank almost exactly backwards by visibility: the layers you see every month (the payment, the pump, the repair quote) are the cheap ones, while the layers you never see (depreciation and opportunity cost) carry most of the true bill. In the 15-year table below, the two invisible rows on the new car together outweigh every visible row combined. So walk the stack in dollar order, heaviest layer first.

• Opportunity cost. The down payment, invested instead, compounds. This is the line item nearly every comparison omits, and it becomes the single biggest row in the table.
• Depreciation. The silent majority of new-car cost. New vehicles commonly lose around 40 percent or more of their value in the first five years, with the steepest drop in years one through three. This is why the used vs new car debate is not close on lifetime cost: the first owner pays for the cliff, the second owner buys the gentle slope.
• Insurance differential. A $45,000 asset costs more to insure than a $6,000 one, and average auto insurance premiums swing widely by driver profile on top of that. Pull real quotes on both vehicles before assuming anything.
• Fuel and fees. Newer cars often sip less fuel, but registration and taxes scale with value.
• Maintenance trajectory. Old cars carry rising repair bills; new cars start cheap under warranty and catch up with age.
• Financing carry. Interest on the loan, plus the car payment opportunity cost, since every payment is money that cannot be invested.

If you doubt the ranking, cross-check it with two independent methods. The IRS standard mileage rate has sat around 67 to 70 cents per mile in recent years, and it exists because the federal government needed an all-in per-mile figure covering fuel, depreciation, maintenance, and insurance. At 12,000 miles a year, that is more than $8,000. AAA's annual ownership study lands in the same neighborhood from the other direction: the average annual cost of owning a new vehicle reached $11,577 in AAA's 2025 figures, about $965 a month. Two unrelated methods triangulating the same order of magnitude, and the payment on the loan statement is only a fraction of it.

Car Total Cost of Ownership Over a 15-Year Runway

The comparison becomes honest only when all three paths run over the same horizon. Fifteen years works well, because it is long enough that every car in the comparison ends up old. The scenario below is built to be easy to audit and easy to swap your own inputs into.

The assumptions

12,000 miles a year, 7 percent real expected return, cash purchases (financing is handled separately below). The keep car is a paid-off sedan worth $6,000. The used replacement is a 4-year-old version of a nicer trim at $21,000. The new replacement is $45,000. Selling the old car funds $6,000 of either purchase, so the incremental portfolio withdrawals are $15,000 (used) and $39,000 (new).

Reading the table

Three things to notice. The new-car path costs about $12,000 a year all-in, which independently confirms the AAA ballpark and shows how far the payment-only view sits from reality. The used path splits the difference, because someone else absorbed the steepest years of depreciation. And the opportunity-cost row alone ($68,600) exceeds the entire depreciation on the new car, which is the thesis in one line: the real cost of a new car is the sticker plus the forgone compounding on it.

Two honesty notes

Only the day-one cash compounds in this table; compounding the monthly differences as well would move the annual figures by a few hundred dollars in this scenario, not thousands. And every input is an assumption you should replace with your own quotes. For model-specific five-year estimates including depreciation and insurance, Edmunds True Cost to Own is the right place to pull real numbers.

The Repair-vs-Replace Crossover Rule

Most "should I repair or replace my car" advice stops at comparing the repair bill to the car's value. The usable answer points the other way: a repair habit is fine until it costs more per year than the replacement would.

The yardstick is the replacement's annual ownership differential, its yearly depreciation plus insurance plus financing measured against the car you already own. In the scenario above, the thresholds look like this:

• Used swap: about $2,600 a year, roughly $1,200 of it depreciation and insurance.
• New swap: about $7,450 a year, about $3,400 of it depreciation and insurance.

Those are the numbers a repair bill has to beat, not the old car's book value.

Worked example: the $3,800 transmission estimate. If the car otherwise runs well and this is a one-off, spreading $3,800 over even five remaining years is about $760 a year, nowhere near the $2,600 threshold, so repairing wins decisively. The answer flips only when repairs become a treadmill, a $2,400-plus quote arriving every year plus rising downtime from tows, rental cars, and missed work. That is the formal line where repairs stop being worth fixing: expected annual repair and downtime spend crossing the differential two years running.

This is also why the popular "repair exceeds car value, so replace it" rule misfires so often. A $3,000 repair on a $4,000 car looks terrible and is still a bargain against a $7,450 annual differential.

Converting the Gap Into Months of FI Date

Dollar gaps do not motivate. Calendars do. The conversion takes two steps.

Step one: state your expected return and compound the diverted cash. Long-run US real equity returns have averaged roughly 6 to 7 percent across very long windows in Shiller's market data, so 7 percent real is a defensible running assumption and 5 percent is the conservative one. At 7 percent, money doubles about every ten years, and $10,000 becomes about $27,600 after fifteen. That multiplier is why the opportunity-cost row grows so large.

Step two: divide the compounded gap by your annual savings. Your FI date arrives when the portfolio crosses your target, roughly 25 times annual spending under the Trinity study's 4 percent rule. For early retirement, savings rate is the denominator that sets the price of every decision, cars included.

How much does a new car delay retirement? In this scenario, set almost entirely by your savings rate: about 28 months if you save $4,000 a month, about 11 months at $10,000. The used swap costs materially less everywhere, about 10 and about 4 months at those same rates.

One refinement for precisionists: if the newer car permanently raises your annual spending, the FI target rises too, by about 25 times the annual increase, which adds still more delay. And if you are within a couple of years of FI, weight the annual expense difference more heavily than the compounding.

Traps That Skew the Math

1. The book-value anchor. Hearing "the repair is 60 percent of the car's value" triggers a replacement instinct, but the relevant comparison is always the replacement's cost differential.
2. Sunk-cost reasoning in both directions. "I've already put $5,000 into it" argues irrationally for keeping, since that money is gone either way, and "it's paid off, so it's basically free to drive" overstates the case too, because an old car still burns depreciation on its remaining value plus rising repairs. The paid-off car is cheapest, not free.
3. Financing above your expected return. The Federal Reserve's G.19 release tracks average auto loan rates, which in recent years have often run above the return many investors expect the market to deliver overall. Borrowing at an APR above your expected nominal portfolio return, your real expectation plus inflation, is a negative-carry trade that lengthens the FI date even when the payment fits the budget, and 72- and 84-month loans are payment engineering built to hide exactly that.
4. Safety-washed lifestyle creep. The honest version prices the upgrade as an upgrade. A $45,000 SUV bought "for safety" when the $21,000 four-year-old version carries the same crash results is a want, and wants are allowed, but they should be declared in months. Financial Samurai ran this exact deliberation with his 2015 Range Rover Sport and chose to keep fixing it, which is what the arithmetic usually says once the full stack is priced.

Run the Numbers on Your Own Car

The whole car total cost of ownership worksheet, in order:

The five steps

1. Inputs. Your car's private-party value, the repair quote, prices for a new and a 4-year-old replacement, live insurance quotes for each (call, do not estimate), fuel costs from fueleconomy.gov's compare tool, your expected real return, your monthly savings, and your years to FI.
2. Three 15-year columns. Depreciation is purchase price minus salvage. Repairs ramp with age; $700 a year rising toward $2,000 is a reasonable old-car spine to adjust from. Add insurance, fuel, and fees.
3. Opportunity cost. Incremental cash out of pocket times about 1.76, since 1.07 to the fifteenth power is about 2.76, so the forgone growth is 1.76 times the principal at 7 percent real.
4. Apply the crossover rule. Divide each replacement's 15-year total by 15 and compare it to the old car's expected annual repair and downtime cost. Below the line, repair. Above it two years running, start shopping.
5. Convert to months. Gap divided by annual savings, times twelve. Then say it out loud: the new one costs 28 months, the used one costs 10.

The verdict on the opening scene

The opening scene resolves cleanly with this worksheet. The $3,800 transmission costs a $4,000-a-month saver roughly one month of FI date. The showroom SUV it was whispering about costs 28. Keep the sedan, drive it gently, and send the difference to the only line in the budget that works while you sleep.