The math I run before I buy.

13 calculators and 20 guides. Every calculator opens already answered, prints each formula with your numbers substituted in, and fits on one printed page you can hand to a lender or a partner. A shared link reopens with the same numbers.

Most calculators return a number and expect it to be trusted. I could not see what counted as an expense, which convention they used, or where the payment came from. A number that is about to go to a lender, a partner or a CPA needs the arithmetic next to it, so every result here shows the formula and the intermediate values. If an assumption does not fit a deal, it is visible.

Every calculator and guide starts from the same example: a $425,000 duplex renting for $3,800 a month, with NOI of $26,220 and a 6.2% cap rate. Financed at 20% down and 7%, it loses $924 a year. I kept it that way on purpose. It is what the math looks like at current loan rates, and the numbers agree on every page.

The formulas are the standard underwriting definitions of NOI, cap rate, debt service coverage and the rest. Where a metric has competing conventions, the calculator says which one it uses. Market figures in the guides come from published sources, including CBRE, Marcus & Millichap, the IRS and the Federal Reserve’s FRED database, and link to them. Without a source, a benchmark does not go on the site.

It does not tell anyone what to buy. It shows what a deal earns, what a lender will see, and what each number leaves out. Tax and legal questions belong to a CPA or an attorney, and the guides that touch them say so. Nothing is behind an email address. The site is supported by ads, not your inbox.

Early. Twenty-five beds is a real portfolio and a small one. I am not selling a course. The student rentals are where occupancy and turnover math matter most, and the short-term rental is where gross revenue says the least until expenses come out. More of my writing is at itsjamesmurray.com.