How do you check a rental property purchase with ChatGPT or Claude?

What to give the assistant

Collect the seller's rent roll and trailing twelve months of income and expenses if they exist, plus the asking price. Add the loan terms you expect (amount, rate, years) and the cash you will put in, including closing costs and any repairs you plan to do on day one.

Remove anything private that the question does not need, such as tenant names. An analysis only needs units, rents, lease dates and amounts.

The prompt

• Here is a seller's rent roll and expense list for a [number]-unit rental priced at [price]. Rebuild the numbers using my assumptions: vacancy [x]%, management [x]% of collected rent even though I will self-manage, repairs and maintenance [x]% of rent, a replacement reserve of $[x] per unit per year, and property tax recalculated on my purchase price at [rate].
• List every line the seller's numbers leave out or understate. Ask me for any number you need instead of guessing.
• Then give me net operating income, cap rate, annual debt service for a [amount] loan at [rate] over [years], annual cash flow, and cash-on-cash return on [cash invested]. Show the formulas.
• Finish with the three assumptions that would change the answer the most.

Asking for the formulas lets you check the work. NOI is income minus operating expenses, and operating expenses do not include loan payments.

What sellers' numbers often leave out

• Vacancy and credit loss. A listing may show every unit paying every month.
• Management. An owner who self-manages shows no management expense, but you may value your time or hire someone later.
• Repairs and reserves. Roofs, water heaters and appliances wear out even if this year's bill was small.
• Property tax. Some places reassess on sale, so the seller's tax bill may be lower than yours.
• Insurance at today's price, not last year's.
• Utilities the owner pays that the rent does not cover.

Compare the seller's expense list line by line with the categories on Schedule E, as described in the IRS Publication 527. A missing category is a question for the seller.

A worked example

Example a made-up 6-unit building is priced at $300,000. Scheduled rent is $36,000 a year. With 5% vacancy, collected rent is $34,200. Operating expenses (taxes, insurance, repairs, utilities, reserves) come to $14,000. Net operating income is $34,200 minus $14,000, which is $20,200. The cap rate is $20,200 divided by $300,000, about 6.7%. A loan costing $13,200 a year leaves cash flow of $7,000. If the buyer puts in $66,000 in cash, cash-on-cash return is $7,000 divided by $66,000, about 10.6%.

Now ask the assistant to rerun it with vacancy at 10% and repairs 20% higher. If the deal only works with the seller's numbers, that is worth knowing before you make an offer.

Verify before you rely on it

1. Check rents against signed leases, not just the rent roll.
2. Check expenses against bills, tax records and the seller's bank statements where you can get them.
3. Recompute NOI and the cap rate with a calculator. Assistants usually do this well but a mis-copied number carries through.
4. Ask a lender or accountant for the loan payment and tax effects. The assistant's estimate is not a quote.

This is arithmetic, not advice on whether to buy. For the terms, see cap rate, cash-on-cash and NOI.

How DoorKeeping handles it

Once you own the property, your assistant can read net operating income by property for any date range straight from the books, so you can compare what the deal promised with what it earns. You can ask for it per property and ask which one is below plan. Rent stays in your own bank account, and anything involving money waits for your approval. DoorKeeping gives no investment or tax advice.

Sources

1. IRS Publication 527: Residential Rental Property, read Oct 30, 2026
2. DoorKeeping: Connect Claude or ChatGPT (steps and tools list), read Oct 30, 2026

Questions

Can ChatGPT tell me if a rental property is a good deal?

It can do the math and flag missing expenses. Whether a deal is good depends on your goals and your market, and the numbers are only as good as what you check.

What cap rate should I look for?

There is no single right number. It varies by market and property type. Compare the cap rate with nearby sales you can verify.

Should I trust the seller's expense numbers?

Treat them as a starting point. Verify against bills and statements, and rebuild missing lines such as vacancy, management, reserves and tax.

Does NOI include the mortgage?

No. NOI is income minus operating expenses. Loan payments come after NOI and affect cash flow.