The true profit on a used car is the sale price minus everything the car cost you — the auction hammer price, buy fees, transport, reconditioning parts and labor, detail, floorplan interest, and your pack — not just "what I sold it for minus what I paid." Most independent dealers who compute margin the short way overstate their per-car profit by $700–$1,500, and it's why a lot that "made money all year" still ends December short on cash.
The formula
Dealers who reconcile to the penny use three-tier gross, the same structure NIADA's chart of accounts assumes:
- Front-end gross = Sale price − Total vehicle cost − Pack
- Back-end gross = F&I income (reserve, VSC/GAP profit, product commissions)
- Total gross = Front + Back
The number that breaks most dealers is Total vehicle cost. It is not one number on a bill of sale — it accumulates over the weeks you own the car:
| Cost bucket | Typical range (per car) | Where it hides |
|---|---|---|
| Purchase price | — | Bill of sale |
| Auction buy fee | $200 – $900 | Auction invoice, often netted into the ACH |
| Transport | $150 – $750 | Carrier invoice, paid weeks later |
| Recon parts | $0 – $1,400 | Parts store statements |
| Recon labor | $0 – $1,100 | Shop invoices — or "free" if it's your own bay (it isn't free) |
| Detail | $120 – $350 | Usually cash, usually never recorded |
| Floorplan interest + fees | $40 – $90 per month held | Lender statement, billed monthly across all cars |
A worked example
You buy a 2019 Equinox at auction for $13,400 and sell it 52 days later for $17,995. "Quick math" says you made $4,595. Now the real ledger:
True front gross: $17,995 − $15,233 − $300 pack = $2,462. Add back-end (say a $900 VSC profit and $350 reserve) and total gross is $3,712 — still a good deal, but 19% less than quick math claimed, and the difference compounds across 15–30 cars a month.
Why days-on-lot is part of the profit formula
Floorplan interest accrues daily, price drops come with age, and a stale unit blocks capital you could roll into the next car. Industry rule of thumb: a unit that crosses 60 days can shed up to 40% of its expected gross between interest, markdowns, and the wholesale exit. Your costing needs a running "days held" clock per VIN, not a month-end guess.
How to actually track this (without a spreadsheet ritual)
- Open a cost ledger per VIN the day you buy. Purchase price, buy fee, transport estimate go in immediately.
- Post every invoice to a car, the day it arrives. A parts receipt that isn't attached to a VIN within a week ends up in "shop supplies" and disappears from your margins.
- Accrue floorplan interest automatically. Daily rate × days held, per unit — reconciled against the lender statement.
- Look at asking price minus live cost, not purchase price. That's your real projected gross while the car sits on the lot, and it should drive your pricing drops.
This is exactly the job a modern DMS should do for you: every cost lands on the VIN as it happens, and the profit you see on screen is the profit you'll see in the bank. That's the entire reason we built live per-car profit in Loturn — the ledger updates itself, and "how much did I actually make on that car?" stops being a research project.