Felix has three rentals and decent equity in his primary residence. To fund the down payment on a fourth property, he opened a $60,000 HELOC at 8.5%, currently in the interest-only draw period. His payment right now is $425 a month — easy to absorb against his $9,000 monthly household income. The $425 isn't the number that matters. What matters is what happens when the draw period ends and the loan converts to full repayment, especially if rates move against him in the meantime.
Two Separate Things Are Changing, Not One
A HELOC used this way carries two risks that often get mentally merged into one: the interest rate can rise, and separately, the draw period will eventually end and the loan shifts from interest-only payments to a fully amortizing payment that includes principal. Either one alone raises the payment. Together, they compound — and the second one happens regardless of what rates do, on a schedule set when Felix opened the loan.
What Felix Is Paying Today
Interest-only on $60,000 at 8.5%: $60,000 × 8.5% ÷ 12 = $425/month. At 4.7% of his $9,000 monthly income, this is comfortable — not the concern.
What Happens When the Draw Period Ends (No Rate Change at All)
Once the draw period ends, Felix owes principal and interest on a standard amortization schedule — this calculator uses 20 years. At the same 8.5% rate, with no hike at all:
Amortizing payment on $60,000 at 8.5% over 20 years: $521/month.
That's a 22.5% jump from $425 to $521 — purely from the draw-to-repayment transition, before considering any rate movement at all. This is the part that catches people off guard: the payment increase isn't contingent on anything going wrong with rates. It's built into the structure of the loan and will happen on schedule.
Stacking a Rate Increase on Top
HELOCs carry variable rates, and a realistic stress scenario is checking what happens at +2 percentage points from today — a move that's well within historical range over a multi-year draw period:
Amortizing payment on $60,000 at 10.5% (8.5% + 2%) over 20 years: $599/month.
That's $599 against Felix's $9,000 monthly income — 6.7% of his monthly income, up from today's 4.7%, and a 41% increase in dollar terms from the $425 he's paying now.
Where That Lands on the Risk Scale
This calculator flags anything under 5% of monthly income as comfortable, 5–8% as worth watching, and above 8% as a real stress point. Felix's stressed scenario (6.7%) lands in the middle tier — within range, but worth watching, not ignoring. A second rate increase, a vacancy on one of his existing rentals, or an unexpected repair bill at the same time would start to compress his margin meaningfully.
The Numbers Side by Side
| Scenario | Rate | Payment | % of Monthly Income |
|---|---|---|---|
| Today (interest-only, draw period) | 8.5% | $425 | 4.7% |
| Draw period ends (same rate, full repayment) | 8.5% | $521 | 5.8% |
| Draw period ends + 2% rate stress | 10.5% | $599 | 6.7% |
Why This Matters More for a Down Payment Than Other HELOC Uses
Using a HELOC to fund a rental property down payment adds a layer that debt consolidation or market investing doesn't carry as directly: the new rental itself has its own cash flow, vacancy risk, and maintenance costs, stacked on top of the HELOC payment risk calculated here. If the new property's cash flow is thin, a HELOC payment that rises from $425 to $599 isn't an isolated line item — it's competing with the same property's own operating costs for the same household cash flow. Running this stress test before closing on property number four, not after, is what turns "the math works today" into "the math still works if two things go wrong at once."
What This Doesn't Include
This models the HELOC payment alone — it does not include the new rental property's mortgage, operating expenses, or expected rental income, all of which affect Felix's actual total monthly obligation and his ability to absorb a payment increase. It's also lender-specific: actual HELOC terms, caps, and whether the draw-to-repayment transition happens on the exact 20-year schedule modeled here vary by lender and loan agreement — confirm your specific terms before relying on this estimate.
Run Your Own Numbers
The draw-to-repayment jump happens to every interest-only HELOC on its own schedule, independent of rates — it's easy to underweight because the current payment feels manageable. Run your own balance, rate, and income through the HELOC Risk Stress Test to see where your specific numbers land before you're relying on the loan to fund a purchase.
Frequently Asked Questions
Why does the payment jump so much just from the draw period ending, even with no rate change?
Because interest-only payments during the draw period cover only the interest charge — none of the $60,000 principal is being paid down. Once repayment begins, the same balance has to be paid off within the remaining loan term, so the payment has to include both interest and a principal portion, which is inherently larger than interest alone on the same balance.
Is 20 years a standard repayment period, or does it vary?
It varies by lender and the specific HELOC agreement — some structure the full term (draw plus repayment) at 10, 15, 20, or 25 years total, with the draw period itself commonly 5–10 years. Felix should confirm his specific loan's repayment-period length with his lender, since a shorter repayment period produces a meaningfully larger payment jump than a longer one on the same balance.
Would it have been safer to take a home equity loan (fixed-rate, fixed payment) instead of a HELOC?
A fixed-rate home equity loan removes the rate-increase risk this stress test checks for, but it doesn't remove the fact that the full principal-and-interest payment starts immediately rather than after an interest-only period — so it front-loads a different version of the same adjustment HELOC borrowers eventually face at the end of the draw period. Which is actually safer depends on whether Felix can comfortably absorb the full payment now versus later, not just on which product avoids a rate hike.
Does using a HELOC for a rental down payment change how the interest is deducted on taxes?
Interest on home equity debt is deductible as a business expense when the borrowed funds are demonstrably used for a trade or business purpose — such as funding a rental property purchase — rather than personal use, which is a different (and generally more favorable) treatment than home equity debt used for personal expenses. Keeping clear documentation that traces the $60,000 directly to the rental purchase is what supports this treatment if ever questioned; mixing HELOC funds with personal spending muddies that trace.
What's the actual mechanism behind "the math still works if two things go wrong at once"?
It means checking the payment under a combined worst case — here, the structural draw-to-repayment jump plus a plausible rate increase — rather than checking each risk in isolation. A borrower who only checks "what if rates rise 2%" while still in the draw period, and separately checks "what's my repayment-period payment at today's rate," can miss that both effects landing together produce a materially larger number than either one alone.