Second Home or Investment Property? IRS Rules Every Florida Keys Buyer Should Know

The IRS draws the line between a second home and an investment property with a calendar, not a mortgage application. In the Florida Keys, where so many purchases are part vacation getaway and part rental income, that day count decides whether rental income is tax-free, whether your deductions are capped, and whether the tax code treats your property as a personal residence or as a rental business. This article walks through the 14-day rule, the personal use test, and how the tax picture lines up with the occupancy rules your lender uses, because the two systems are related but they are not the same.

If you have not yet sorted out the financing side of this decision, start with my guide to primary vs second home vs investment property financing. This article is about the tax classification, when it shifts, and how to keep it straight alongside your mortgage.

Two Different Systems: The IRS and Your Lender Classify Your Home Differently

Before any day counting, it helps to know that you are managing two separate classification systems at the same time. Your lender classifies your property by occupancy: primary residence, second home, or investment property. That drives your loan program, down payment, interest rate, and reserve requirements, and I explain the full comparison in my three-way financing guide.

The IRS classifies the same property by its own rules in the tax code: how many days you rented it at a fair price, how many days you used it personally, and which number is bigger. The two systems borrow similar language, but the thresholds are not identical, and a property can be a second home for your mortgage and a rental property for your taxes in the same year. That is normal, and it is manageable, but only if you know which hat you are wearing when.

The 14-Day Rule: Rent 14 Days or Fewer and Keep the Income Tax-Free

The single most useful rule for Keys owners is the IRS 14-day rule, formally part of Section 280A(g) and commonly called the Augusta rule. If you rent out a home you also use personally, and that home is rented for fewer than 15 days in the tax year, the rental income is completely tax-free. You do not report it, and you do not pay income or self-employment tax on it, no matter how much you charge per night.

The trade-off is that you cannot deduct any rental expenses for those days either, no cleaning fees, management fees, or depreciation. You keep your normal homeowner itemized deductions, including the mortgage interest and property taxes for the home. For a Keys owner, this is a clean seasonal play: rent your Key West cottage for a week during Fantasy Fest, rent your Key Largo canal house for a spring break week, and the money is yours with no tax form involved.

One warning that catches people: there is no partial credit. The rule works only under 15 rental days. Rent on the 15th day and the entire year's rental income becomes taxable, with no prorating. The 14-day threshold is a cliff, not a ramp.

Day 15 and Beyond: Now You Count Every Night

Once you rent the home 15 days or more in a year, the rental income is taxable, and you have to count days carefully because the next threshold determines how much you can deduct. From here the IRS asks one question: is this a residence, or is it a rental property? The answer comes from the personal use test.

The Personal Use Test: 14 Days or 10 Percent

For a home rented 15 or more days, the IRS treats it as a residence (what most people call a vacation home) if your personal use days exceed the greater of:

• 14 days, or
• 10 percent of the days it was rented at a fair rental price.

Personal use days are broader than people expect. A day counts as personal use if you or a co-owner stays there, if family members stay there (unless a family member uses it as their main home and pays a fair rental price), if it is rented at less than fair market value, or if it is used under a reciprocal arrangement where someone else's home is available to you. Days you spend substantially full time repairing or maintaining the property do not count as personal use, and days the home simply sits vacant and available for rent do not count as rental days.

Here is what those thresholds look like in real Keys numbers. If you rent your Marathon home 60 nights a year at fair rental, 10 percent is 6 days, so the test is the 14-day floor. Use it personally 15 nights and the IRS calls it a residence. If you rent it 200 nights a year, 10 percent is 20 days, so personal use above 20 nights pushes it into residence territory. The more you rent, the more personal use the code tolerates before calling it a vacation home.

Vacation Home Status: Deductions Capped at Rental Income

When the IRS treats your Keys property as a residence, you must allocate expenses between rental use and personal use, typically by days. The rental portion of mortgage interest, property taxes, utilities, insurance, maintenance, and depreciation is deducted on Schedule E, in a specific order: interest and taxes first, then other expenses, then depreciation. And here is the catch that shapes most Keys planning: those rental deductions cannot create a rental loss. They are limited to the gross rental income for the year.

Practically, that means a vacation home rented part time rarely produces a tax loss, even though the cash flow might look negative. The unused rental expenses do not carry over. For many Keys owners this is simply the cost of keeping a home in the family, and the right framing is that they are getting rental income with no taxable gain once it is consumed by the allocated expenses.

Rental Property Status: When the Tax Code Calls It a Business

If your personal use does not exceed the greater of 14 days or 10 percent of fair rental days, the IRS treats the property mainly as a rental. Now the rental deductions can exceed rental income, producing a deductible rental loss, subject to the passive activity loss rules. That is where depreciation over 27.5 years and, for aggressive owners, cost segregation enter the picture, which I cover in my ranking of homeowner tax write-offs.

The trade-off is that the property is no longer a residence for tax purposes. You lose the second-home treatment for mortgage interest (more on that below), and rental losses may be limited unless you actively participate or qualify as a real estate professional. This is squarely tax-return territory, so a CPA who knows vacation rentals is worth the fee before you structure a rental-heavy purchase.

Where Mortgage Interest and Property Taxes Actually Land

Whenever there is any personal use, you split the big home deductions by day count:

• The rental share of mortgage interest and property taxes goes on Schedule E as a rental expense, inside the income cap described above.
• The personal share goes on Schedule A as itemized deductions, mortgage interest for a second home and property taxes subject to the state and local tax (SALT) deduction cap.

For the personal share of interest to qualify as deductible second-home mortgage interest, IRS Publication 936 requires that you personally use the home more than 14 days or more than 10 percent of the rental days in the year. Notice that this is the same 14-days-or-10-percent shape as the residence test. If your personal use falls below that line, the property is a rental for tax purposes and your interest deduction follows rental rules instead. Second-home interest is also subject to the $750,000 acquisition debt limit when combined with your primary home debt, which matters in a market like Monroe County where loan balances are routinely high.

This is the point where the tax calendar and the lender's occupancy rules meet. My guide to renting out your Keys home explains the lender thresholds, and the 14-day personal use figure shows up on both sides, which is no accident: the drafters borrowed the same logic. But the lender is not the IRS, and the IRS is not the lender, so you track both.

How the Day Count Lines Up With Your Mortgage

Here is the practical overlap for a Keys buyer. On the mortgage side, a second home under conventional guidelines means personal use with no rental management agreement, no pooling arrangement, and no advertising as a short-term rental that limits your control, with occasional renting permitted. Step up to a heavily rented property and lenders want investment property treatment: bigger down payments, higher rates, and rental income that can help you qualify. DSCR loans go further and qualify the loan entirely on the property's income, which is often the cleanest fit for a Keys vacation rental, and my DSCR guide covers when that makes sense.

The dangerous zone is the middle: a home rented heavily enough that the IRS treats it as a rental, financed with a second home loan. That mismatch is occupancy fraud, and it does not survive scrutiny. Lenders verify occupancy through inspections, utility records, and tax returns, and the consequences include loan acceleration. If your plan involves significant rental income, finance it honestly: second home loans for personal-use getaways, vacation home loans for the occasional rental scenario, and investment property loans or DSCR when the rent is the point.

The Keys Reality: Local Vacation Rental Rules on Top of the Federal Ones

Before you base a purchase on rental income, remember that the Florida Keys add their own layer of local rules on top of the IRS and the lender. A few things every buyer should check for the specific property:

• Monroe County tourist development tax. Short-term rentals of six months or less are subject to a 5 percent tourist development tax, and for most vacation rentals the owner, not the booking platform, is responsible for collecting and remitting it to the Monroe County Tax Collector.
• Key West. Vacation rental licenses are capped, and new licenses generally are not issued unless one is surrendered. Buying a condo in Old Town does not automatically come with the right to rent it short term, so verify the license situation for the exact unit before you write an offer.
• Islamorada. Vacation rentals need an annual license and registration, with an application fee, and rentals in residential zoning commonly require a 7-day minimum stay.
• Marathon. Licensed short-term rentals generally operate in the 7 to 28 night range, with rentals under 7 nights prohibited.
• Unincorporated Monroe County. Rules vary across the islands from Big Pine Key to Tavernier, so confirm with the county and the HOA before assuming the property can be rented at all.

These rules change, and HOA documents can be stricter than the city. Treat local verification as part of due diligence, on the same level as the appraisal and the survey.

A Simple Day-Counting Checklist

For owners and buyers who want to stay out of trouble, keep a running count in a spreadsheet or a note on your phone:

• Nights rented at a fair rental price, with the income recorded.
• Nights you or a co-owner stayed at the property.
• Nights family or friends stayed, unless they paid fair rent from a main home of their own.
• Nights rented below market rate, which count against you as personal use.
• Nights spent substantially full time on repairs and maintenance, which do not count as personal use.
• Whether you crossed 14 rental days, which triggers the whole day-counting regime.
• Whether personal use exceeds 14 days or 10 percent of fair rental days, which decides residence vs rental status.
• And separately, the occupancy you declared on your mortgage application, so the loan and the tax return tell the same story.

Sort This Out Before You Buy

The Florida Keys market runs on second homes and rentals, which means the difference between a tax-free two-week rental and a full investment property is a real decision, not a paperwork detail. Get the plan straight before you make an offer, and make sure the financing matches the plan.

I work with Keys buyers across every occupancy type, from full-time residents in Key West to seasonal owners in Islamorada to rental investors in Marathon. Let us talk through your situation, your rental plan, and your timeline, and I will show you the loan structure that fits. For the tax specifics, bring a CPA into the conversation early; the mortgage and the tax plan should be designed together.

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The second home vs investment property decision is one of the most common conversations I have with Keys buyers, and the tax classification is half of it. Whether you are buying a personal getaway that might earn a few weeks of tax-free rental income, or a property built to produce income, the right structure starts with an honest plan.

Bring me your plan, and I will bring you the loan options that fit it. We will sort the mortgage, and you bring the plan to your CPA for the tax return.

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