Prompt details

Tested on

Claude Opus 5.5

Length

512 words · 3 fill-ins

Example input

[The car and the prices you found]: I want a 2024 Toyota RAV4 Hybrid XLE (about 2 years old). Three listings within 40 miles: A. Lakeside Toyota: 28,400 miles, Toyota Certified Used. Listed at $33,900. Small print: "plus $799 dealer service fee and $1,495 ProShield protection package (pre-installed)". B. Desert Auto Group (not a Toyota dealer): 22,100 miles, not certified. Listed at $32,750, "plus $599 doc fee". Clean history report shown, one owner. C. Valley Toyota: 35,800 miles, Toyota Certified Used. Listed at $32,400. Fees not shown online. I test drove A and liked it. I don't need the car for 2 to 3 weeks.

[Your trade-in]: 2015 Honda Civic LX sedan, 112,000 miles, paid off, clean title, minor scratches on the rear bumper, tires about half worn. An online car buyer gave me an instant offer of $7,200, valid for 7 days. Lakeside Toyota said they'd give me "around $5,500" for it.

[Budget and financing]: I live in Mesa, Arizona. I think sales tax here is around 8%, but I'm not sure exactly. Cash down: $3,000 plus the trade-in. Credit union pre-approval: up to $32,000 at 6.49% APR for 60 months. Credit score about 740. I want the monthly payment at or under $520, and I'd rather not go over $36,000 out the door before the trade-in. I drive about 12,000 miles a year.

Example output

1. Budget check

Payment formula: M = L × r ÷ (1 − (1 + r)^−60), where r = 6.49% ÷ 12 = 0.0054083.

This works out to $19.5615 per $1,000 borrowed (factor 0.0195615).

*Assumption: you sell the Civic to the online buyer for $7,200, so cash plus trade equals $10,200.*

Item	Figure	Math
Max loan your $520 payment supports	$26,583	520 ÷ 0.0195615
Max out-the-door (OTD) that payment supports	$36,783	26,583 + 3,000 + 7,200
Your own OTD cap (before trade)	$36,000 ← this is the binding limit
Payment at $36,000 OTD	$504.69/mo	(36,000 − 10,200) = 25,800 × 0.0195615
Total interest at $36,000 OTD	$4,481	504.69 × 60 − 25,800
Total interest at the $520 maximum	$4,617	520 × 60 − 26,583
If you trade to Lakeside at $5,500 instead	Max OTD drops to about $35,083	26,583 + 3,000 + 5,500
Rough monthly running cost (estimates to verify)	About $300–$380	See breakdown below

Running cost breakdown (all rough estimates):

Fuel: about $90. That is 1,000 mi ÷ about 39 mpg ≈ 26 gal × [add gas price]; I used about $3.50.
Insurance: about $120–$200 [add your quote].
Maintenance: about $40.
Arizona vehicle license tax: about $40–$60 a month equivalent.

Your $32,000 pre-approval is not the limit. The $520 payment and the $36,000 cap are. Keep the term at 60 months, and don't stretch it to make a payment fit.

2. Out-the-door worksheet

Tax = (Price + taxable dealer fees + add-ons) × [add rate]. I used your 8% estimate below; replace it with the actual Mesa combined rate. Whether doc fees are taxable is something to confirm for your state.

Title and registration = R [add title & reg]. Arizona's vehicle license tax is based on value. A rough estimate is $500–$800 for this car (verify with ADOT MVD), and I used R ≈ $600 in the illustration rows.

	A. Lakeside (CPO)	B. Desert Auto	C. Valley (CPO)
Price	$33,900	$32,750	$32,400
Dealer fees	$799	$599	F [ask]
Add-ons	$1,495 ProShield	$0	[ask]

Claude Opus 5.5

Negotiate a Car Price – Car buying prompt for ChatGPT and Claude

^$9.99

Kept in your account
Copy filled in or download
Updates included

Pay once and keep it. Or get every premium prompt and skill with the plan, $19.99 a month. Payments are non-refundable. See our Terms.

votes views

Claude Opus 5.5

This prompt plans a car purchase and negotiation. Paste the listings you found, your trade-in and your budget; you get an out-the-door worksheet, target and walk-away prices, a quote email and scripts for the dealer.

What you get

A budget check with the payment and total interest at your rate
An out-the-door worksheet for every listing, with target and walk-away numbers
A quote request email and replies to the dealer's usual moves
A finance office add-on table and a signing-day checklist

How to use it

1
Collect the listings and a trade-in offer
Save each listing's price and fine print, and get at least one outside offer for your trade-in.
2
Send the email to every dealer
Ask each one for a written, itemized out-the-door quote, and compare the quotes in the worksheet.
3
Bring the checklist on signing day
Check every number in the contract against the agreed quote before you sign.

Better results

Each time a written quote comes in, paste it and ask: "Recalculate the worksheet with this dealer's quote."
Get your trade-in offer in writing before you negotiate, so the dealer's number has a floor.
If a dealer will only talk monthly payments, ask for the out-the-door figure in writing or move on to the next dealer.

Questions

Can ChatGPT help me buy a car?

Yes. ChatGPT, Claude or Gemini can compare listings on out-the-door price, do the loan math, write quote request emails and prepare you for the finance office. It works from the figures you give it, so confirm taxes and fees locally. It cannot promise a price.

What is an out-the-door price?

The out-the-door price is the total you pay for the car: the vehicle price plus dealer fees, any add-ons, sales tax, and title and registration, minus your trade-in. Comparing dealers on this one number stops fees and add-ons from hiding in the deal.

Which dealer add-ons should I decline?

Decline add-ons you did not ask for, such as paint and fabric protection, VIN etching or nitrogen-filled tires, unless you want them at a price you agreed. An extended warranty or GAP coverage can suit some buyers, but compare prices outside the dealer first.

Is there a cooling-off period when you buy a car?

Usually not. The FTC's Cooling-Off Rule does not cover cars bought at a dealer's lot, and most states give no right to return a car once you sign. Some dealers offer a return policy; get it in writing before you buy.

Updated 8 Nov 2026