Decision 1: Accepting the Dealer’s Rate Without Shopping
A buyer accepts 9.5% from dealer financing without knowing their credit union offered 6.5%. On $30,000 for 60 months: 9.5% = $628/month/$7,680 interest. 6.5% = $586/month/$5,160 interest. The 15 minutes not spent getting a credit union quote cost $2,520.
Decision 2: Extending to 72 Months for a 'Comfortable' Payment
A buyer stretches to a $42,000 SUV by choosing 72 months instead of 60. 60-month payment at 8%: $852. 72-month payment at 8.5%: $745. The $107 monthly savings cost an extra $1,476 in interest, 12 extra payments, and 12 more months of being underwater on the vehicle.
Decision 3: Not Checking Trade-In Value Before Entering the Dealership
A buyer with a $14,000 car accepts a dealer trade offer of $10,500 without checking KBB or getting a Carvana/CarMax offer first. The $3,500 difference was never recouped in the vehicle negotiation — it was just given away.
Car purchase decisions and the cost of not running the numbers
| Decision | Cost of Not Calculating | Time to Calculate |
|---|---|---|
| Accepting dealer rate without shopping | $1,500–$4,000 in extra interest | 2 hours |
| Choosing 72 months over 60 | $1,000–$2,500 in extra interest | 5 minutes |
| Not checking trade-in value | $1,000–$5,000 given away | 30 minutes |
| Not researching out-the-door price | $500–$3,000 in dealer markup | 1 hour |
| Financing extras at F&I office | $2,000–$6,000 over life of loan | 5 minutes to decline |
Run the Numbers Before You Decide
Enter your target vehicle price and compare rate and term scenarios — know exactly what you’re committing to.