ARM vs Fixed on a Rental: Pricing the Rate Bet

An adjustable-rate mortgage on a rental is a trade: you collect a known discount for a fixed number of years, and in exchange you hold the rate risk afterward. Like any bet it has a price, a payoff and a worst case, and all three can be computed before you sign.

On the example $300,000 rental in this post, a 7/6 ARM priced 0.625 points under the fixed rate is worth $9,885 by the end of year seven. If the first reset then lands at the cap, the payment jumps $674 a month and that entire edge is gone in 17 months. Whether the bet is worth taking depends almost entirely on one thing: whether you will still own the loan when it resets.

The 2026 spread: what an ARM saves today

This post does not quote current rates. The spread between ARM and fixed pricing moves with the shape of the yield curve, and any number printed here would age badly. When short-term rates sit well below long-term rates, ARMs price at a real discount. When the curve is flat or inverted, the discount shrinks to almost nothing, and sometimes ARMs price above fixed loans.

So measure it yourself. Ask one lender, on one day, for a 30-year fixed quote and a 7/6 ARM quote on the same property with the same points. Subtract. Then use this table, built on a $225,000 loan against an example 7.00% fixed rate, to see what your spread is worth.

The 84-month column is the rounded monthly figure times 84.

Here is the honest reading. At a quarter point, you are being paid $38 a month to carry the full rate risk on a 30-year loan. That is not worth taking, and you should say no without further analysis. At half a point the bet is marginal and only suits a short, firm hold. Around three quarters of a point and above, the savings start to pay for the risk. If your quotes come back with a thin spread, the right move is the fixed loan and no regrets.

One more fact about the rental market: many investment property ARMs come from portfolio and DSCR lenders, not the conventional channel. Those loans can carry prepayment penalties, which matter a great deal for a strategy built on refinancing. Ask before comparing rates.

ARM anatomy: fixed period, caps, index, margin

A "7/6" ARM is fixed for 7 years and then adjusts every 6 months for the remaining 23. Four terms in the note control what happens after year seven.

Index. The market rate the loan follows. New ARMs commonly use a 30-day average of SOFR. You cannot negotiate it and nobody can predict it.

Margin. A fixed number of points the lender adds to the index, set at closing for the life of the loan. An example margin is 3.00 points. Two ARMs with the same start rate and different margins are different loans, and the one with the lower margin is better for every year after the fixed period.

Fully indexed rate. Index plus margin. This is the rate the loan wants to charge at each adjustment, before caps. If the index is an example 4.75% and the margin is 3.00, the fully indexed rate is 7.75%.

Caps. Three limits, usually written as three numbers. A common structure on a 7/6 ARM is 5/1/5:

• The first adjustment can move the rate up to 5 points above the start rate.
• Each adjustment after that can move it up to 1 point from the prior rate.
• The rate can never exceed 5 points above the start rate.

Read your own note, because cap structures vary. Notice what 5/1/5 means: the lifetime cap can be reached at the very first reset. A start rate of 6.375% can become 11.375% on the first day of year eight. Many notes also set a floor, often equal to the margin, so the rate cannot fall without limit.

At each adjustment the lender takes the remaining balance and re-amortizes it over the remaining term at the new rate. That is the calculation in the next section.

The worked bet: 7/6 ARM vs 30-year fixed on a $300,000 rental

Every rate here is a labeled example. The property costs $300,000 with 25% down, so the loan is $225,000. Net operating income is $1,900 a month. The fixed offer is 7.00%. The 7/6 ARM offer is 6.375% with 5/1/5 caps and a 3.00 margin.

Years one through seven

The ARM wins twice. The payment is $93 lower, and because a lower rate sends more of each payment to principal, the balance is $2,073 lower after seven years. The total is $7,812 + $2,073 = $9,885. If you sell or refinance at or before month 84, you keep all of it, less any costs of the exit.

The first reset, in whole dollars

At month 85 the lender re-amortizes $203,009 over the remaining 276 months at the new rate. The fixed loan's payment stays at $1,497.

The caps math in plain dollars: at the cap, the ARM payment rises from $1,404 to $2,078. That is $674 more a month, or $8,088 a year, arriving in a single adjustment. Monthly cash flow goes from $496 to -$178. The payment is $581 above the fixed loan you could have taken, and $9,885 / $581 means the savings from seven good years are spent in 17 months.

The middle row deserves attention. Even if rates do not move at all, a loan with a 3.00 margin resets to the fully indexed rate, which in this example is 7.75% and above the fixed rate you turned down. An ARM's start rate is usually a discount to its own fully indexed rate. A reset higher is the default outcome unless the index falls, and only the size is in doubt. Compute your fully indexed rate on the day you get the quote: if it is already above the fixed offer, the ARM is a seven-year coupon and nothing more.

After the first reset the rate moves every six months by up to 1 point, up or down, and the payment is recalculated each time. Budgeting on a rental gets harder when the largest expense changes twice a year.

The scenarios that break the ARM case

The plan behind most ARMs is "I will refinance or sell before the reset." The bet breaks when that exit is closed at the moment you need it.

Rates are higher and you cannot refinance out. If rates are up at year seven, the refinance you planned is at a higher rate too, so the exit does not help. You are choosing between the reset rate and a new fixed loan at that day's prices, plus closing costs.

The value fell with the rate rise. The conditions that push your payment up also push property values down, because buyers pay less for the same income when debt costs more. How interest rates move cap rates explains the mechanism. For an ARM holder these risks arrive together: a higher payment, a lower appraisal, and a smaller sale price, all in the same year. A refinance needs loan-to-value and DSCR to work at the new rate, and both have just gotten worse.

The hold ran long. Plans to sell in year five become year nine because of a tenant, a soft market or a tax reason. Every ARM borrower planned to be out before the reset.

Exit costs eat the edge. A refinance at year seven costs money. If it runs an example $5,500, more than half of the $9,885 edge goes to closing costs, and you restart a 30-year clock. A prepayment penalty can consume the rest.

The spread was thin to begin with. At a quarter point discount the seven-year edge on this loan is about $4,000 including the balance difference. There is no bad scenario that small a prize can absorb.

Who should take the bet: hold horizon decides

The decision variable is how long you will hold this loan, and how certain that is.

An exit at month 60 on the example still banks a real sum: $93 x 60 = $5,580 in payments, plus a balance that is $1,477 lower ($211,796 on the fixed loan against $210,319 on the ARM), for $7,057 total. That is the clean version of the bet. You take the discount, and you are gone two years before the rate can move.

The long-term holder gets the worst version. Seven years of savings worth $9,885 are set against 23 years of exposure on a roughly $200,000 balance. For a buy and hold investor, the fixed rate is the insurance premium that makes the rest of the pro forma believable, and the example shows it costs $93 a month.

Stress-test the reset before you sign

Do this with the actual term sheet in hand.

1. Write down the start rate, margin, index, caps and any floor or prepayment penalty.
2. Compute the fully indexed rate today. Compare it with the fixed quote.
3. Estimate the balance at the end of the fixed period and re-amortize it over the remaining term at three rates: fully indexed, start rate plus 3 points, and the cap.
4. Put each payment against your NOI. Note the DSCR and monthly cash flow in each case. Any case under 1.0 is a month you fund from savings.
5. Divide your total edge by the monthly overage in each case to get the number of months the savings last.
6. Decide what you would do in the cap case. If the answer is "refinance," check that the property would qualify at that rate. If the answer is "sell," assume a lower price.

The single family calculator will run the property at any rate and payment you enter, so you can see cash flow and DSCR at the start rate and at each reset rate. The sensitivity analysis feature does it in one grid: set the interest rate axis to span your best case, your fully indexed rate and the cap, and the cap-rate-hits-you case is sitting next to the expected one. For more on reading those grids, see sensitivity analysis for real estate deals.

If the deal survives the cap column with a DSCR you can live with, take the discount. If it only works in the left half of the grid, pay for the fixed rate and spend your risk budget somewhere it earns more.