Using a HELOC to buy a rental property: the math that has to work

A HELOC against your own home is the most common way small landlords find a down payment without selling anything or saving for another two years. You draw on the equity in the house you live in, use the cash to buy a rental, and finance the rest of the purchase with a separate mortgage on the rental. On paper it is fast money you already own. In practice it stacks two debts against one stream of rent, and one of those debts has a rate that moves.

Almost every page that ranks for this is written by a bank, a lender, or a short-term-rental company that benefits when you say yes. So the downside math stays vague. The number that actually decides the deal is one nobody runs in full: the HELOC payment plus the new mortgage payment against the rental's monthly cash flow, including what happens when the HELOC rate climbs. That double-payment stress test is the whole of this page.

How the structure actually works

Start with the equity in your primary residence. Lenders usually let you borrow up to a combined loan-to-value of 80% to 85% across your first mortgage and the new line. Say your home is worth $500,000 and you owe $300,000. At an 85% combined cap, total debt can reach $425,000, so the HELOC ceiling is about $125,000. That is the pool you can draw from, not a balance you have to take all at once.

You then use a draw from that line as the down payment on the rental. Say you buy a single-family rental for $250,000 with 25% down, the typical floor for an investment property. The down payment is $62,500, which you pull from the HELOC, and a separate rental mortgage covers the remaining $187,500. If you are unsure why the rental wants 25% rather than the smaller number on an owner-occupied loan, that gap is covered in how much down payment you need for an investment property. The HELOC funds the equity slice; the mortgage funds the rest.

The double-payment math that has to work

Here is the part the lender pages skip. You now owe two payments tied to one rental. Run them both against the rent before you sign anything.

Take the $250,000 rental above. The $187,500 rental mortgage at a labeled hypothetical 7.5% over 30 years runs about $1,311 a month in principal and interest. The $62,500 HELOC draw at a labeled hypothetical 9% interest-only payment runs about $469 a month during the draw period. That is $1,780 a month in financing alone, before taxes, insurance, or a single repair.

Now the rent. Say the unit rents for $2,100 a month. Knock off a 5% vacancy factor and 35% for taxes, insurance, maintenance, and the reserve you should be holding, and you are left with roughly $1,260 of income to cover financing. Against $1,780 of payments, that is negative $520 a month. The deal that looked like free equity is a property you feed $6,240 a year to keep. The point is not that HELOC-funded deals never work. The point is that the second payment is real and most spreadsheets only show the first.

For the deal to clear, either the rent has to be higher, the purchase price lower, or the HELOC paid down fast from another source. Run your own numbers through a cash-on-cash calculator with both payments included, not the mortgage alone, and through a cap rate calculator to check the property on its own merits.

The variable rate is the real risk

A HELOC rate is tied to a benchmark index plus a margin, so it moves when rates move. The fixed mortgage on the rental does not flinch, but the HELOC payment can climb after you have already bought the property and committed the rent. Stress test it. If the HELOC rate on the $62,500 draw rose from a hypothetical 9% to 12%, the interest-only payment goes from about $469 to about $625 a month, another $156 a month out of a deal that was already underwater in the example above.

The other clock is the draw period. Most HELOCs allow interest-only payments for the first 10 years, then convert to a repayment period where you amortize the balance over the remaining term. When that flip happens, the payment jumps hard, because you are suddenly paying down principal too. A landlord who built the whole plan on the interest-only number gets a payment shock years in. Underwrite the repayment-period payment, not the teaser. A line of credit feels free right up until the index turns.

HELOC, home equity loan, or cash-out refinance

Three tools draw on the same equity and solve different problems.

• A HELOC is a revolving line you draw and repay at will during the draw period, at a variable rate. It fits a short hold: buying a property you plan to fix and refinance out of within a year or two, where you want to pull the balance back to zero and reuse the line.
• A home equity loan is a lump sum at a fixed rate with a fixed payment. It fits a down payment you intend to carry for years, because you trade the flexibility of a line for the certainty of a rate that will not move.
• A cash-out refinance replaces your whole first mortgage with a bigger one and hands you the difference. It fits when current rates are at or below your existing rate, so resetting the whole loan does not cost you the cheap mortgage you already have.

The full side-by-side on pulling equity through a refinance, including the loan-to-value caps and the seasoning clock, lives in the cash-out refinance on a rental property guide rather than here. If you want the wider menu of ways to fund the purchase, including conventional and DSCR options, start with the guide to financing a rental property.

The tax rule everyone gets wrong

The most-botched claim in competing posts is that HELOC interest is deductible because it is secured by your home, or not deductible because it is not a mortgage on the rental. Both miss the rule. Deductibility follows the use of the money, not the collateral, under the interest tracing rules described in IRS Publication 527. If you spend the HELOC draw to buy or improve a rental, the interest on that draw traces to the rental and is deductible on Schedule E, even though the lien sits on your primary home.

The flip side is the cost of mixing the money. If you draw $62,500 for a rental down payment and another $20,000 for a kitchen in your own house off the same line, only the rental slice of the interest is a rental deduction. The personal slice traces to a personal use and is not deductible at all. That makes a clean record of every draw and exactly where it went the difference between an easy deduction and an indefensible one. Keep the proceeds for the rental separate, ideally a dedicated draw used for nothing else, so the tracing is obvious if it is ever questioned.

Tracking two loans against one property

Once you close, the recordkeeping problem is permanent: one rental, two loans, and one of them has a payment that changes. You need each payment split into deductible interest and non-deductible principal, and you need the HELOC interest to show up in the rental's true cash flow even though it is secured somewhere else. Get that split wrong and you either overstate the deduction by writing off principal or understate the cost of the deal by ignoring the second payment. The mechanics of keeping interest, principal, and escrow straight are in tracking mortgage interest, principal, and escrow correctly.

This is the seam where I built rents.ai for myself: it supports more than one loan per property, so the HELOC draw and the new rental mortgage both feed the same property's cash flow and equity picture, each payment split into interest and principal automatically. It will not shop the line, pull a live HELOC rate, or warn you when the index moves, so the rate watching is still on you. What it does is keep two loans from drifting out of one number once the deal is done.