How to compare the performance of your rental properties by asking AI
Ask for net operating income, vacancy and expenses for each property over the same twelve months, with the rent per unit beside them. Compare per unit and as a percent of income, not in raw dollars, because a small building and a large one cannot be judged by totals. Then look at the weakest one and ask why.
The five numbers worth comparing
| Number | What it tells you | Ask for it as |
|---|---|---|
| Net operating income (NOI) | Income left after operating costs, before the mortgage. See how to calculate NOI. | Total, and per unit per month |
| Vacancy | How many days units sat empty and what that cost. | Days vacant and lost rent |
| Expenses | Where the money goes: repairs, insurance, taxes, utilities. | Percent of income, by category |
| Rent per unit | Whether rents match the building and the market. | Average, with the range |
| Late or unpaid rent | How much rent was owed and not collected. | Amount and number of tenants |
Use the same twelve months for every property. A property that had a new roof in one year will look worse than one that did not, so keep that in mind when you read it.
A prompt to start with
"For the last twelve full months, show each property as a row: units, NOI, NOI per unit per month, vacancy loss, expenses as a percent of income and average rent. Sort by NOI per unit. Tell me which numbers you could not find."
The last sentence is the useful part. If expenses for one property are missing, or a bill was not categorized, the comparison is unfair, and you want to know that before you draw a conclusion.
Reading the result fairly
- Compare per unit. A 4 unit building and a 40 unit building should be judged by what each unit earns.
- Separate one-time costs. A big repair is real, but it is not the same as a steady expense. Ask for the result with and without it.
- Look at vacancy before rent. A property with low rent and full units can beat one with high rent and long gaps.
- Check the books are current. A comparison is only as good as the last time you categorized bills and matched deposits.
Example a made-up owner has two buildings. Building A has 8 units and an NOI of $52,800 a year, which is $550 per unit per month. Building B has 20 units and an NOI of $96,000, which is $400 per unit per month. Building B earns more in total, but each unit of A earns more. The owner asks why B lags and finds the cause is two units that sat empty for four months each.
What to do with the weakest property
- Find out which number is off: income, vacancy or expenses.
- Ask the assistant to list the biggest expense lines for that property and any bills filed under an odd category.
- Check rents against what units there are asking now. See how to price a listing.
- Decide on one change and look again in a quarter.
If you file taxes with these numbers, remember that income and expenses for each property go on your own return as shown in the IRS Schedule E instructions. Ask your tax preparer how to treat a one-time repair.
How DoorKeeping handles it
Your assistant can read net operating income by property for a date range, the T12 with one column per month, vacancy per unit and the profit and loss, all from the same books. DoorKeeping keeps a separate set of books for each property, so each row of the comparison comes from its own ledger. Totals are computed in code in whole cents. Reports can also be downloaded as a spreadsheet or PDF.
Sources
- IRS: About Schedule E (Form 1040), Supplemental Income and Loss, read Oct 30, 2026
- DoorKeeping: Connect Claude or ChatGPT (steps and tools list), read Oct 30, 2026
Questions
- What is the best number to compare rental properties?
- NOI per unit per month is a good starting point because it adjusts for size. Read it together with vacancy and expenses as a percent of income.
- Can ChatGPT compare my rental properties?
- Yes, when it is connected to your records. Without a connection it only works with numbers you paste in.
- How often should I compare my properties?
- Quarterly is enough for most owners. Use twelve months so seasonal changes do not mislead you.
- Why does one of my properties look worse than it is?
- A one-time repair, an uncategorized bill or a long vacancy can distort a year. Ask for the numbers with and without those.