Real Estate Calculators

The full deal analysis: purchase, financing, rent, vacancy, and expenses in — monthly cash flow, cash-on-cash return, and cap rate out. Operating expenses exclude the mortgage; the payment is computed for you from the price, down payment, rate and term. The definitions chain and a property walked through it are below. For the field-by-field walkthrough and the FAQ, see the dedicated Rental Property Calculator page.

Compare the true net cost of renting versus buying over the years you plan to stay — equity, appreciation, selling costs, and (when you enter them) purchase closing costs included. The comparison is simulated month by month; how, and why the years-to-stay field matters so much, is explained below. Full guide on the dedicated Rent vs. Buy Calculator page.

The definitions chain: NOI, cap rate, cash flow, cash-on-cash

Every rental figure on this site is built from one short chain of definitions, in one order, and each link reuses the one before it. Start with effective rent: monthly rent × (1 − vacancy%). Vacancy is a steady haircut rather than a count of empty months, so a 6% allowance removes 6% of every month's rent. Next, net operating income (NOI) = (effective rent − operating expenses) × 12. Operating expenses exclude mortgage principal and interest by industry convention — the convention to get right when you fill in the form — so NOI describes what the property earns regardless of how it is financed. Cap rate = NOI ÷ property value, and is therefore financing-independent too. Only then does the loan enter. Cash flow = effective rent − operating expenses − mortgage payment, per month, where the payment comes from the standard amortized-loan (PMT) formula with monthly compounding; a 0% rate divides the principal evenly. Last, cash-on-cash return = annual cash flow ÷ cash invested, and cash invested is the down payment + closing costs + initial rehab: the cash that actually left your pocket, not the purchase price.

One property, walked through the chain

Take a property entered as a $275,000 purchase with $55,000 down, a loan at 6.5% over 30 years, $2,450 of monthly rent, a 6% vacancy allowance, $790 of monthly operating expenses, $6,500 of closing costs and $4,000 of initial rehab. Effective rent is $2,303.00. Subtracting the operating expenses and annualizing gives an NOI of $18,156, which against the $275,000 price is a 6.6% cap rate. The $220,000 loan costs $1,390.55 a month, so monthly cash flow is $122.45 ($1,469 a year). Cash invested is $65,500, and $1,469 ÷ $65,500 is a 2.24% cash-on-cash return. Every one of these numbers was produced at build time by the same engine that runs the two calculators above; none was typed.

Now change one input at a time and watch which links move. Raise the down payment to $96,250 (35% of the price) and the loan shrinks: the payment falls to $1,129.82, cash flow rises to $383.18 a month, and cash-on-cash becomes 4.31% on $106,750 invested — while NOI stays $18,156 and the cap rate stays 6.6%, because neither contains the loan. Pay all cash and there is no payment at all: cash flow equals NOI ÷ 12, $1,513.00 a month, and cash-on-cash is 6.36% — close to the cap rate but below it, since the closing costs and rehab sit in the denominator alongside the price. Set the vacancy allowance to 0% instead and the chain moves from the top: effective rent becomes $2,450.00, NOI $19,920, cap rate 7.24% and cash flow $269.45 a month. That is the mechanism behind two rules worth keeping in mind: cap rate is financing-independent while cash-on-cash is not, and anything that changes effective rent or expenses changes every number downstream.

Three screens, and why a screen is not a verdict

Ahead of the full chain, the site offers three shortcuts. Each deliberately ignores most of the inputs above, which is what makes it quick — and what makes it a screen rather than a verdict. The 1% rule asks whether monthly rent reaches 1% of the purchase price. On the walk-through property the target rent is $2,750 and the entered rent of $2,450 is 0.89% of the price, so the screen reports that it falls short of the line; a $180,000 property entered with $1,900 of monthly rent sits at 1.06% against a $1,800 target and clears it. Neither result knows anything about vacancy, expenses or financing — the walk-through above shows how much those decide — so the screen's only output is whether the full analysis is worth running, and it cannot say what that analysis will find.

The gross rent multiplier (GRM) is price ÷ gross annual rent. Monthly rent is annualized first, so $2,450 a month is $29,400 a year and the walk-through property's multiplier is 9.35 — equivalently, 112.2 months of gross rent to equal the price. Entering the same rent as an annual figure gives the identical multiplier (the build checks this), which matters because a multiplier of monthly rent would be twelve times larger and the two bases are easy to mix up. The reverse mode runs the same arithmetic backwards: gross annual rent × a multiplier gives an estimated value, and feeding the walk-through property's own rent and multiplier back in returns $275,000, the price we started from. GRM uses gross rent before vacancy and before any expense, so two properties with the same multiplier can have very different NOI and cap rates: it compares listings on what they collect and says nothing about what they keep.

The 70% rule is the flipping convention: maximum offer = rule% × after-repair value − rehab costs, with 70% as the default and the percentage yours to change. For a flip entered with a $320,000 after-repair value (ARV), $45,000 of rehab, a $185,000 purchase price, $9,000 of holding costs and selling costs of 6% of the ARV, the rule's maximum offer is $179,000; set the rule to 65% and it becomes $163,000. The projected profit is a separate calculation that ignores the rule entirely: ARV − purchase − rehab − holding − selling costs, here $320,000 less $258,200 of total cost (including $19,200 of selling costs) = $61,800, or 23.93% of that total cost. Notice that the entered purchase price sits above the rule's ceiling and the profit line still computes: the two outputs do not police each other, which is exactly why the rule is a convention and not a verdict. The gap the rule leaves between the maximum offer plus rehab and the ARV has to absorb the holding and selling costs the profit line subtracts before any of it is profit.

How the rent-vs-buy comparison is simulated

There is no single formula behind rent vs. buy. The calculator keeps two running totals and moves them forward one month at a time for as many years as you say you will stay. The renting total is the simpler of the two: each month's rent is added, and once a year that rent steps up by the growth rate you entered. The buying total opens with the cash paid on day one — the down payment, plus purchase closing costs if you entered any, as either a percent of the price or a dollar figure (not both), paid up front rather than added to the loan, and zero unless you fill the field in. It then adds every mortgage payment and, each month, the ownership costs charged at your annual percentage of a home value that rises once a year by the appreciation rate. When the horizon ends, the buying total is credited with what a sale would hand back: the appreciated price, minus selling costs, minus whatever loan balance the amortization schedule says is still owed. Whichever total is lower is the cheaper path. For a comparison entered as $1,700 of rent growing 2% a year against a $300,000 home with $60,000 down, purchase closing costs of 3% of the price ($9,000), a 6.5% mortgage over 30 years, ownership costs of 2% of value a year, 1.5% appreciation and 6% selling costs: over 3 years renting totals $62,432 and buying nets $78,402 after $63,480 of sale proceeds come back, so renting comes out cheaper by $15,970; over 12 years the same inputs give $273,607 against $221,386, and buying comes out cheaper by $52,221. Nothing changed but the horizon. The costs at both ends are paid once and spread across the stay, while the loan balance falls slowly at first and faster later, which is why the years-to-stay field matters so much in this comparison.

What nothing on this site models

Every number on this page is a screen or a plan, not an underwriting result, and the shortest honest description of each calculator is the list of what it leaves out. Look back at the walk-through property: its 6.6% cap rate and 2.24% cash-on-cash were built from the rent, the vacancy allowance, the operating expenses and the loan, and from nothing else. The rental functions have no field for appreciation on the property, for principal paydown counted as part of the return, for income taxes or depreciation deductions, for PMI or financing points, for rent growth on the investment property, or for market cycles — so none of those is in the result, and the engine does not guess at how much any of them would add or take away. The rent-vs-buy comparison has blind spots of its own: it does not ask what the down payment could have earned elsewhere, does not touch how mortgage interest is taxed, and adds purchase closing costs only when you type them in. The fix-and-flip profit uses the holding and selling costs you entered and nothing more, and the rehab budget adds up your line items without supplying a cost for anything. An absent factor is absent, not approximated, which is why a result here describes the inputs you entered rather than predicting what the property will do. The methodology page keeps the authoritative list, and the guide What these models leave out walks it calculator by calculator.

The common misreadings

Four misreadings are worth naming, because each is a correct definition applied in the wrong place. Putting the mortgage into operating expenses. The payment is computed separately from the price, down payment, rate and term, so entering it again as an expense counts it twice. Do that to the walk-through property — add its $1,390.55 payment to the $790 of expenses — and NOI collapses to $1,469, the cap rate to 0.53% and the monthly cash flow to -$1,268.10, all three wrong. Reading cap rate as the return on your money. Cap rate is the property's yield on its price with no loan; cash-on-cash is the return on the cash you invested after the loan is paid. The walk-through shows the same property at a 6.6% cap rate and 2.24%, 4.31% or 6.36% cash-on-cash depending only on the financing. Treating a screen as an answer. The 1% rule and GRM use gross rent and ignore expenses and financing; the 70% rule's margin has to absorb holding and selling costs before any of it is profit. Ignoring the horizon. A rent-vs-buy result is only meaningful for the number of years you entered; the same inputs can favor renting at one horizon and buying at another, as the simulation above shows.

Start here

The two calculators on this page are the same engine as their dedicated pages, which add field-by-field walkthroughs and their own FAQs: the Rental Property Calculator and the Rent vs. Buy Calculator. The rest of the directory isolates one link of the chain or one screen each: the Cap Rate Calculator, the Cash-on-Cash Return Calculator, the Gross Rent Multiplier Calculator, the 1% Rule Calculator, the Fix & Flip Calculator and the Rehab Budget Calculator.

The guides explain each piece at length, with every figure computed by the engine:

• NOI and cap rate, explained — effective rent, operating expenses without the mortgage, NOI, and what cap rate omits.
• Cash flow and cash-on-cash return — the mortgage payment, cash invested, and why financing changes one number but not the other.
• The 1% rule and GRM as screens — what each ratio looks at and what it ignores.
• The 70% rule for flips — the maximum offer, the projected profit, and the rule percentage as a convention.
• Rent vs. buy: how the simulation works — the month-by-month model, closing-cost handling, and the horizon.
• What these models leave out — the omissions, calculator by calculator.

The methodology page holds the definitions above in their authoritative form, and the about page explains the site's scope. The reference case the engine's automated tests check — a $220,000 purchase with $44,000 (20%) down at 7% over 30 years, $2,200 of rent, 5% vacancy, $650 of monthly expenses, $5,000 of closing costs and $3,000 of rehab — recomputes here as a $1,170.93 payment, $269.07 of monthly cash flow, 6.21% cash-on-cash and a 7.85% cap rate. If a number ever looks wrong, the contact page is the place to report it.

Frequently asked questions

Not financial advice: these calculators provide general educational estimates that exclude taxes, appreciation variability, and local market factors. Verify any deal with your own due diligence and qualified professionals. Everything is processed locally in your browser and never transmitted. How every formula works — and what each model leaves out — is documented on the methodology page.