A 1-percentage-point mortgage rate rise can outrun 4 years of rent growth

The Federal Reserve raised interest rates on Sept. 16 for the first time since 2023. For rental property investors, the bigger issue is how long borrowing costs stay elevated while rents grow slowly.

A Griffin Funding scenario analysis shows how small changes in mortgage pricing can outpace years of rent growth. On a $300,000 loan, increasing the mortgage rate from 6.75% to 7.75% raises the rent needed to maintain the same debt coverage by 8.3%. That is equivalent to about 4.5 years of growth at July's 1.8% annual single-family rent pace, holding other assumptions constant.

Key findings

* In the modeled purchase, raising the mortgage rate from 6.75% to 7% requires about 2% more rent to maintain the same debt coverage, equal to roughly 14 months of growth at a constant 1.8% annual pace.

* Raising the rate from 6.75% to 7.75% requires 8.3% more rent, equal to about 4.5 years of growth at that pace.

* The Federal Reserve raised rates on Sept. 16, and now projects rates will stay higher through 2027 than it expected in June.

* For debt-service coverage ratio (DSCR) borrowers, a lower coverage ratio can change the available loan amount, down payment or financing terms.

The Fed's outlook may matter more than the hike

The Fed's policy committee voted 12-0 to lift the federal funds target range to 3.75% to 4%, citing elevated inflation. Nobody dissented.

For investors, the committee's new projections matter more than the hike. The median official now sees the federal funds rate at 4.1% at the end of both 2026 and 2027, up from 3.8% and 3.6% in the June projections. The same projections don't show inflation returning to the Fed's 2% goal until 2029. Policymakers now expect higher rates for longer than they did three months ago. Investors hoping to wait out today's borrowing costs may be waiting a while.

The Fed doesn't set mortgage rates, but the bond market listens

A Fed hike doesn't change anyone's mortgage rate overnight. Mortgage rates track the bond market, and traders had priced in better than a 90% chance of this increase before it happened.

That anticipation has been lifting borrowing costs for weeks. The 10-year Treasury yield hit its highest level since 2007 the day before the decision. Mortgage News Daily's 30-year fixed rate climbed to 7.19%, more than a percentage point above a year earlier. Freddie Mac's weekly survey, which tracks owner-occupied buyers with 20% down and strong credit, reached 6.95% on Sept. 17, up from 6.76% a week earlier and 6.26% a year ago. Investment property loans generally price above that benchmark.

Rents are moving far more slowly

Single-family rents, the main income for small landlords, rose 1.8% over the year through July, below the 2.3% pace a year earlier, according to Cotality. Growth has now picked up for five straight months, though it remains below historical averages, and it is uneven: Chicago led major metros at 5%, while Houston managed 0.2%. Across all rental types, Apartment List found the national median rent was still 0.8% below its level a year before in August, although it has now risen seven months in a row.

A mortgage quote can change in a day. Rent growth takes time.

How DSCR math turns rates into rent

Residential DSCR financing evaluates qualifying rental income relative to principal, interest, property taxes, insurance and association dues, alongside other borrower and property requirements. A ratio of 1.0 means rent equals that payment. This analysis uses 1.25, meaning rent is 25% higher, as an illustrative target rather than a universal lending requirement. Because the ratio compares rent with the payment, keeping it steady means rent has to rise by the same percentage the payment does.

Griffin Funding modeled a $300,000, 30-year fixed loan, roughly a $400,000 purchase with 25% down, plus $500 a month for property taxes, insurance and association dues.

Going from 6.75% to 7% raises the payment by about 2%. At 1.8% annual rent growth, rents need about 14 months to close that gap. Going from 6.75% to 7.75% raises the payment by about 8.3%. Closing that gap takes about 4.5 years.

The dollar amounts scale with loan size. A quarter point adds roughly $43 per month to principal and interest on a $250,000 loan and about $172 on a $1 million loan.

How it plays out on one purchase

Consider a hypothetical purchase. An investor is under contract on a $400,000 single-family rental expected to lease for $3,000 a month, with 25% down. At 6.75%, her coverage ratio is about 1.23. At 7%, it slips to 1.20. At 7.25%, it's 1.18. At 7.75%, it falls to about 1.13. The house and the rent never change. At 7.25%, reaching the illustrative 1.25 target would require about $3,183 in qualifying monthly rent, $183 above her expected $3,000. Alternatively, keeping rent unchanged, she could reduce the loan to roughly $278,500 by adding about $21,500 to her down payment.

That additional cash becomes equity in the property, not a fee. But it is cash she can no longer keep on hand for repairs, vacancies or another purchase. Rent growth might narrow the gap over time. The additional down payment would have to be available at closing.

This is an illustrative example, not an actual borrower.

The same rent can support a smaller loan

The Fed's projections are individual participants' views, not a set policy path. The property-level math is more immediate. In this model, higher mortgage pricing reduces the loan amount that $3,000 in monthly rent can support at the selected coverage target. The buyer can contribute more equity or negotiate a lower purchase price, and different financing terms may also change the calculation.

That is the gap between rent growth and borrowing costs. Rent may rise over years, while the buyer has to meet the financing terms at closing. The house doesn't have to get more expensive for the cash needed to buy it to go up.

Methodology

Payment figures are Griffin Funding calculations for a $300,000, 30-year, fully amortizing loan at each rate shown, plus a flat $500 per month for taxes, insurance and association dues. Rent needed equals the monthly payment multiplied by 1.25, an illustrative assumption rather than a lending standard. Because required rent rises in proportion to the payment, years of rent growth were calculated by comparing the percentage payment increase with Cotality's 1.8% annual single-family rent growth (July 2026), compounded annually. The rent-growth comparison is not a forecast and does not measure the recovery of cumulative cash flow or investment returns. Loan-size figures compare principal and interest at 7.50% and 7.75% for each loan amount shown. All figures are illustrative and don't represent any lender's rates, pricing or qualification terms, which vary by credit, leverage, property type and loan structure. Changes in the federal funds rate don't translate one-for-one into mortgage or DSCR loan rates.

This story was produced by Griffin Funding and reviewed and distributed by Stacker.

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