What a Real Estate Calculator Tells You That the Listing Doesn't

Listing pages advertise the rent. The rent is the top line, and the top line is the least informative number in the deal. What matters is what survives the mortgage, the tax bill, the empty months, and the boiler.

The three numbers a calculator gives you

Cash flow, cap rate, and cash-on-cash

Cash flow is rent minus every outgoing including the mortgage, per month. It tells you whether the property costs you money to own, which decides whether you can hold it through a bad year.

Cap rate ignores the mortgage entirely: net operating income divided by purchase price. Stripping out financing lets you compare two properties bought on different terms, or a building against a savings rate.

Cash-on-cash is annual cash flow divided by the actual cash you put in. It answers the question an investor cares about most, which is what your own money earned rather than what the asset earned.

One property, worked through

A $250,000 house, 25 per cent down. That is $62,500 plus around $6,000 in closing costs, so $68,500 leaves your account on day one. The $187,500 loan at 7 per cent over 30 years costs $1,247 a month.

Rent is $2,000. Now the outgoings: property tax $290 a month, insurance $110, maintenance budgeted at 8 per cent of rent ($160), vacancy at 6 per cent ($120), and management at 8 per cent ($160). Operating costs total $840. Add the mortgage and you are paying out $2,087 against $2,000 coming in.

Cash flow is negative $87 a month. The cap rate is still respectable: net operating income of ($2,000 minus $840) times 12 is $13,920, divided by $250,000, or 5.6 per cent. The asset is fine. The financing is what makes it bleed, and that is why you run both numbers.

A UK version: a £180,000 flat let at £1,100 a month has a gross yield of £13,200 divided by £180,000, or 7.3 per cent. Take off service charge, ground rent, letting fees, and mortgage interest and the net figure typically lands two to three points lower.

The costs people leave out

Vacancy is the big one. Assume 100 per cent occupancy and every projection looks great. A single void month a year is already 8.3 per cent off the rent. Then come capital items, the roof and the boiler and the windows, which never show up monthly but arrive eventually and cost thousands.

How to use the real estate calculator

Work top to bottom: purchase price, down payment or deposit, interest rate, term, monthly rent, then each running cost on its own line. Then change one input at a time to see what the deal is sensitive to. On the example above, rent of $2,150 flips the cash flow positive, while a rate of 7.5 per cent pushes it to about negative $150.

Where each input comes from

Price and property tax come from the listing and the county or council record, both public. Rent should come from what comparable units nearby are currently let at, not from what the seller says is achievable. Get a real insurance quote rather than guessing. Management is a genuine cost even if you self-manage, because your time is not free and you may not always want the job. Our guide to rental calculators goes further on the metrics, and the rent versus buy comparison frames the same money differently.

Common questions

What counts as a good cap rate? It depends on the market and is only meaningful against local alternatives. In expensive metros 4 per cent is normal, which on the $250,000 house above would mean net operating income of $10,000 a year rather than $13,920; in cheaper markets 8 per cent is common and carries more risk. Compare a property to others in the same city, never to a national average.

Does price appreciation count as a return? It is real, but it is a forecast, not income. Keep it out of the cash flow calculation and treat it as upside. A deal that only works if the property gains value is a bet, not an investment.

Why does the calculator say negative when the agent called it a strong yield? Because gross yield ignores the mortgage, vacancy, and maintenance. A gross yield of 9.6 per cent and cash flow of negative $87 can describe the same house on the same afternoon.

Should I include my own labour? Yes, priced at what it would cost to hire out. Otherwise you are counting unpaid weekends as profit, and the numbers collapse the moment you stop.