A real investment property calculator needs more than just purchase price and expected rent to be trustworthy. Most online calculators oversimplify, which is exactly why two investors can plug in the same property and walk away with two very different affordability numbers.
The Core Numbers a Calculator Needs
- →Purchase price and down payment percentage
- →Interest rate and loan term
- →Expected monthly rent, based on real comparable rentals, not a guess
- →Property taxes and insurance (Texas has no state income tax, but property taxes run higher than the national average)
- →A realistic vacancy rate, typically 5-8% even for a well-managed property
- →A maintenance and capital expenditure reserve, usually 8-12% of rent
- →Property management fees, if you are not self-managing (typically 8-10% of rent)
- →Any planned renovation or repair budget, added to your total cash needed
Sample DFW Math
| Line item | Monthly amount |
|---|---|
| Rent income | $2,200 |
| Mortgage (P&I, 25% down, current rates) | -$1,050 |
| Property tax + insurance | -$450 |
| Vacancy reserve (6%) | -$132 |
| Maintenance reserve (10%) | -$220 |
| Property management (9%) | -$198 |
| Net cash flow | ~$150 |
Why Do Two Investors Get Different Numbers From the Same Property?
Almost always, it comes down to what they left out - usually vacancy, maintenance reserves, or renovation costs. A property that looks like $400 a month in cash flow using only rent minus mortgage often turns into $100-$150 once every real expense is included, which is why the eight inputs above all matter, not just the two obvious ones.
Pro tipThe renovation and repair line is the one number that most calculators guess at, and the one number a licensed contractor can give you exactly. Get a real bid before you finalize your affordability math.
Running the numbers on a DFW property? Get a free, real construction estimate to plug into your calculator.
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