Buying a condo to rent out is a different exercise from buying one to live in. You are not buying a view or a lobby; you are buying a stream of cash flows, and the building either produces them reliably or it does not. Serious investors underwrite that stream with a repeatable method — the same handful of inputs, run the same way, every time — so the decision rests on arithmetic rather than on how the model unit was staged. Here is that method applied to a Miami condo. It deals in how to gather and combine the inputs; the actual current numbers for any building or neighborhood belong to that building's documents and to our live report at /market-stats, never to a rule of thumb.
Underwrite the unit, not the view
The first discipline is to value the specific unit as an income asset. Two lines in the same tower can underwrite completely differently once you account for their rent, their dues and their financing, so resist pricing the building and price the unit. Everything below reduces to one question: after every real cost of owning and operating this unit, what cash does it put in your pocket, and what return does that represent on the money you put in? Hold that question and the rest is bookkeeping.
Step one: the rent the unit can actually command
Start with gross rent — the annual income the unit realistically produces, not the number a listing agent hopes for. You establish it from genuine comparables: what similar lines in the same and neighboring buildings are actually leasing for right now. In Miami this is where the seasonal reality matters, because winter-season demand can lift rents in a way an annualized figure has to average out. Do not invent this number and do not borrow it from a different market; pull current leasing comps and let our /market-stats report frame where the neighborhood's rents and pricing sit. Everything downstream is only as honest as this first input.
Step two: the operating expenses that decide the deal
Next, subtract every cost of operating the unit that is not your mortgage. For a Miami condo that list is longer than newcomers expect: the association's monthly dues, property taxes, your own HO-6 insurance, a vacancy allowance for the weeks between tenants, property management if you are not self-managing, and a small reserve for in-unit repairs and turnover. Property taxes deserve special care, because a rental is not your homestead — you do not get the homestead exemption or its assessment cap, so a non-homestead investor's tax line runs higher than an owner-occupant's on the identical unit; our homestead guide explains exactly why. The dues line, meanwhile, is the one that most often decides a Miami deal, which is why it gets its own section below.
NOI, cap rate and cash-on-cash, in plain terms
With those two figures you can compute the numbers that actually compare deals. Net operating income, or NOI, is simply gross rent minus operating expenses, before any mortgage. Divide NOI by the purchase price and you have the capitalization rate — the unlevered yield the unit throws off, and the cleanest way to compare one building against another. Then layer in financing: subtract the annual mortgage payment from NOI to get pre-tax cash flow, and divide that by the actual cash you invested — down payment plus closing costs — to get cash-on-cash return, which tells you what your invested dollars earn. Cap rate compares assets; cash-on-cash measures your position. A method that produces both, from real inputs, beats any single headline yield.
The HOA and assessment reality that breaks Miami pro formas
Nowhere does a Miami rental pro forma go wrong faster than on the association. Monthly dues in an amenity-rich coastal tower can consume a large share of gross rent before you have paid a cent of tax or debt, so a unit that looks cheap per square foot can underwrite poorly once its dues are in the model. Then there is assessment risk: after Florida's post-Surfside reforms, associations of covered buildings must fund Structural Integrity Reserve Studies and can no longer waive reserves for major structural components, and a building that deferred that work can levy a five-figure special assessment that erases a year of cash flow. Underwrite the dues as they are today and read the reserve study and assessment history before you assume they will hold; our guide to reading a condo budget walks through the exact lines to pull.
Financing, warrantability and the rental rules you must verify
Two building-level facts can make or break the deal after the arithmetic looks fine. The first is warrantability: lenders treat a condo project as warrantable or not based on things like owner-occupancy ratios, reserves, litigation and single-owner concentration, and a non-warrantable building means higher rates, a larger down payment, or portfolio financing — all of which change your cash-on-cash. The second is the building's own rental rules. Many Miami associations cap how often a unit may be leased, set minimum lease terms, or restrict short-term rental outright, so the short-stay income some buyers pencil in may simply not be permitted. Verify the leasing rules in the declaration before you underwrite anything short-term; our guide to pet-friendly and Airbnb-friendly Miami buildings is a starting point, but the association's own documents are the authority.
Stress-test it before you sign
Finally, do not underwrite to a best case. Run the same model with a higher vacancy assumption, a dues increase at the next budget, a softer winter rent, and an interest rate a point higher than quoted, and see whether the unit still clears your target return. A deal that only works when every input breaks your way is not a deal; it is a hope. The strength of this method is that it forces each assumption into the open, where you can pressure-test it. Gather the real inputs — leasing comps, the association's budget and reserve study, the tax record, a real financing quote — combine them the same way every time, and let /market-stats and the building's own documents supply the figures. The arithmetic, done honestly, tells you whether a Miami condo is an investment or just an address.
Questions investors ask about underwriting a Miami condo
How do I calculate a Miami condo's cap rate?
Take gross rent, subtract every operating expense that is not your mortgage to get net operating income, then divide NOI by the purchase price. That gives the unlevered yield the unit throws off and is the cleanest way to compare one building against another. Cash-on-cash is the separate figure: subtract the annual mortgage payment from NOI, then divide by the cash you actually invested.
Which expenses do investors forget on a Miami condo?
The list is longer than newcomers expect: association dues, property taxes, your own HO-6 insurance, a vacancy allowance for the weeks between tenants, property management if you are not self-managing, and a reserve for in-unit repairs and turnover. Property taxes deserve special care, because a rental is not your homestead — without the homestead exemption or its assessment cap, an investor's tax line runs higher than an owner-occupant's on the identical unit.
Why do HOA dues break Miami rental pro formas?
Because monthly dues in an amenity-rich coastal tower can consume a large share of gross rent before you have paid a cent of tax or debt, so a unit that looks cheap per square foot can underwrite poorly once its dues are in the model. Assessment risk compounds it: a building that deferred structural work can levy a five-figure special assessment that erases a year of cash flow.
Can I short-term rent a Miami condo I buy as an investment?
Not necessarily. Many Miami associations cap how often a unit may be leased, set minimum lease terms, or restrict short-term rental outright, so the short-stay income some buyers pencil in may simply not be permitted. Verify the leasing rules in the declaration before you underwrite anything short-term, because the association's own documents are the authority.
How should I stress-test the numbers?
Run the same model with a higher vacancy assumption, a dues increase at the next budget, a softer winter rent, and an interest rate a point higher than quoted, then see whether the unit still clears your target return. A deal that only works when every input breaks your way is not a deal.
Written by
Miami Condo HQ
Miami Condo Specialists
Miami Condo HQ is a Miami condo platform — in-depth profiles for the condo buildings we track across Miami, for-sale and for-rent listings, building profiles and Miami market research, and honest, pressure-free guidance for buyers, sellers and investors across South Florida.
