The Equation Everyone Skips
A new vs used car cost calculator only earns its name if it runs this equation, and almost none of them do:
True cost = depreciation + loan interest + insurance + repairs + fuel + sales tax
Six terms. The price on the windshield is not one of them. It feeds the first term and the last, and that's the whole of its influence. Yet the price is the number every buyer anchors on, which is why the used-car decision so often disappoints: people compare one term of a six-term equation and expect the answer to hold.
Run all six and something awkward turns up. On the default comparison in the calculator above — a $38,000 new car against a $26,000 three-year-old version of it, held five years — the used car wins. It just wins by a lot less than the sticker promised, and it loses three of the six categories outright.
$12,000 Off the Sticker, $7,967 in Your Pocket
That's the problem in one line. The two cars are $12,000 apart on price. After five years of ownership the real gap is $7,967 — you keep 66% of the discount you thought you were getting. The other $4,033 evaporates into interest, repairs and fuel. Here is the full ledger:
| 5-Year Cost | New ($38,000) | Used ($26,000, age 3) | Winner |
|---|---|---|---|
| Depreciation | $19,172 | $8,215 | Used by $10,957 |
| Loan interest | $6,606 | $7,612 | New by $1,006 |
| Insurance | $10,500 | $8,250 | Used by $2,250 |
| Maintenance & repairs | $2,992 | $7,182 | New by $4,189 |
| Fuel (32 vs 28 MPG) | $6,188 | $7,071 | New by $884 |
| Sales tax (7%) | $2,660 | $1,820 | Used by $840 |
| Total | $48,118 | $40,150 | Used by $7,967 |
Read the Winner column, not the Total row. The used car takes $14,047 across depreciation, insurance and tax — then hands $6,079 of it straight back through interest, repairs and fuel. That clawback is the entire story of this decision, and it is invisible in any tool that stops at monthly payment. Per mile, the two land at $0.80 and $0.67; per month of ownership, $802 against $669. If you want the same six-term treatment for a single vehicle you already own, our total cost of car ownership calculator runs it without the comparison.
Why the Cheaper Car Pays More Interest
This is the line that stops people. The used buyer finances $23,820. The new buyer finances $35,660— nearly twelve thousand dollars more. And the used buyer still pays $1,006 more in total interest over the same 60 months.
A 4.6-point APR gap does that. Used-car loans price above new ones for a structural reason: a lender that repossesses a six-year-old car recovers far less than one that repossesses a one-year-old car, and that recovery risk gets priced into the rate. Manufacturers also subsidize new-car financing to move inventory. Nobody subsidizes used. The result is a spread that widens sharply as credit weakens:
| Credit tier | New-car APR | Used-car APR | Spread |
|---|---|---|---|
| Superprime (781–850) | ~5.2% | ~7.4% | 2.2 pts |
| Prime (661–780) | ~6.4% | ~9.6% | 3.2 pts |
| Nonprime (601–660) | ~9.6% | ~14.1% | 4.5 pts |
| Subprime (501–600) | ~13.0% | ~18.9% | 5.9 pts |
| Deep subprime (300–500) | ~15.4% | ~21.6% | 6.2 pts |
Rounded industry averages for 60-month loans. Your quote is the number that matters — use it in the calculator.
Note what the Spread column does. A superprime buyer pays a 2.2-point penalty for going used; a subprime buyer pays 5.9. The buyers with the strongest reason to shop used are the ones charged most for it. If your score sits in the bottom two rows, get the rate quoted before you pick the car — the CFPB's auto loan guide explains how to shop financing separately from the vehicle, which is the single highest-value hour in this process.
The Used-Car Advantage Has a Shelf Life
Hold both cars longer and the used car's lead does not keep growing. It peaks in year four at $8,147 and then shrinks every year after. Nobody tells buyers this, because it only shows up when you model depreciation and repair spend on the same timeline:
| Years held | New total | Used total | Used advantage |
|---|---|---|---|
| 3 years | $35,021 | $27,149 | $7,873 |
| 4 years | $42,129 | $33,982 | $8,147 ← peak |
| 5 years | $48,118 | $40,150 | $7,967 |
| 8 years | $63,926 | $57,852 | $6,074 |
| 12 years | $84,583 | $83,622 | $961 |
The mechanism is a race between two curves. Depreciation is front-loaded — the new car burns roughly 20% in year one and only 7–8% a year by year five, so its disadvantage is largest early and flattens fast. Repair spend runs the other way, compounding as parts reach service life. By year twelve the used car is a fifteen-year-old vehicle absorbing $24,169 in cumulative repairs, and the $12,000 head start is gone. Our car depreciation calculator maps the first curve on its own; the car maintenance cost calculator handles the second.
The practical reading: buying used and keeping it about four years captures nearly all of the available advantage. Buying used and keeping it fifteen years is a lifestyle choice, not a financial one.
3 Inputs That Decide the Whole Answer
Seventeen fields sit in the calculator above. Three of them move the verdict; the rest are rounding. Change these and re-run before you trust any result.
1. The used car's age.This is the biggest lever, because age decides which slice of the depreciation curve you buy. Holding the price at $26,000, a one-year-old car loses $11,024 over five years and beats the new car by only $5,158. A seven-year-old car loses $5,776 and wins by $10,406 — double the advantage from the same purchase price. The sweet spot most buyers want sits at three to five years old, where the steepest depreciation is already someone else's loss but the repair curve hasn't turned yet.
2. The used APR you actually qualify for. Every point matters more than buyers expect. At 6.9% the used car wins by $11,167. At 11.5% it wins by $7,967. At 15% the margin collapses to $5,399— an 8.1-point rate swing erases $5,768 of advantage without changing a single thing about either vehicle. Credit-union preapproval typically beats dealer-arranged financing by one to two points, which is worth more here than negotiating $500 off the price.
3. Your repair budget.The default assumes $1,200 in year one for the used car, escalating 9% annually to $7,182 across five years. Under-budget this and the used car looks artificially good. A three-year-old car still inside a 5-year/60,000-mile powertrain warranty is a genuinely different risk than the same car at 90,000 miles with nothing left, even though both are "three years old" on paper. The FTC's Used Car Rule guidance covers the Buyers Guide window sticker that tells you exactly what warranty, if any, comes with the car.
When Buying New Actually Wins
Four situations flip this, and the calculator will show you which one you're in.
Subsidized financing you qualify for.Manufacturer 0% offers are the one force strong enough to fight depreciation. Set the new car's APR to 0% in the calculator and its five-year total drops from $48,118 to $41,512. In this particular matchup that still isn't enough — the new car remains $1,362 more expensive — but narrow the sticker gap to $9,000 instead of $12,000 and free money wins outright. Always run the stress test rather than assuming.
A used market that hasn't normalized.When a three-year-old car costs 82% of new instead of 68%, you're paying new-car money for used-car risk. Check the ratio before anything else; our used car value calculator gives you the benchmark to test the asking price against.
Very high annual mileage.At 25,000 miles a year the fuel line stops being a footnote. A 4-MPG deficit costs $884 over five years at 12,000 miles annually — and $1,842 at 25,000. Add faster wear on an already-worn car and the gap narrows further. Check the EPA figures for both vehicles at fueleconomy.gov rather than trusting the listing.
You cannot absorb a $3,000 surprise.This one isn't arithmetic. A transmission failure in month fourteen doesn't care that the used car is $7,967 ahead on a spreadsheet. If the repair would go on a 24% credit card, the warranty on the new car is buying something the model can't price.
What Changed Since 2021
The used-car case is weaker than the received wisdom because two things moved at once. In 2021 the average new-car loan ran near 5% and used near 8.5% — a 3.5-point spread on an already-cheap base. By 2025 those had climbed to roughly 7% and 11.5%, and the dollar cost of the spread grew with them. On our $23,820 used balance, going from 8.5% to 11.5% adds about $2,100 in interest over 60 months.
Used values moved too. The supply shock that began in 2020 pushed used prices up sharply against new, and while that premium has eased, three-year-old cars still hold a larger share of their original value than the pre-2020 norm. Higher retained value is exactly what a used buyer does notwant: it means the previous owner ate less of the depreciation, and the discount you inherit is smaller. Both shifts point the same direction, and both are reasons to run the numbers on your actual quote rather than trusting a rule of thumb formed in a 4%-interest decade. Once you've picked a side, the car sales tax calculator pins down the tax line for your state, and the car payment calculator confirms the monthly figure your lender should be quoting.