A 5-year adjustable rate mortgage is a home loan that carries a fixed interest rate for its first five years and then adjusts at set intervals for the rest of the term. The initial rate is usually lower than a comparable 30-year fixed mortgage, which makes the early payments smaller. After year five, the rate resets against a market index, and your payment moves with it. You get a discount now in exchange for accepting uncertainty later.
The Two Phases of the Loan
Every 5-year ARM has a fixed phase and an adjustable phase. For the first 60 months, your interest rate is locked. Your monthly principal and interest payment stays the same regardless of what happens in financial markets, and you can budget with full confidence during that window. Lenders offer the lower starting rate because they are shifting interest-rate risk to you once the fixed period ends.1U.S. Department of Housing and Urban Development. FHA Adjustable Rate Mortgage
Once the five years expire, the loan enters its adjustable phase. Your rate is recalculated at set intervals through the end of the term, and your monthly payment changes to reflect the new rate. How often that recalculation happens depends on which version of the product you have.
5/1 vs. 5/6: What the Second Number Means
The number after the slash tells you how often your rate resets during the adjustable phase. A 5/1 ARM adjusts once a year. A 5/6 ARM adjusts every six months. Both lock in the same five-year fixed period up front.
This distinction matters more than it used to. Fannie Mae and Freddie Mac, the two government-sponsored enterprises that buy most conforming mortgages, now require SOFR-indexed ARMs with six-month adjustment periods rather than annual ones.2Freddie Mac. SOFR ARMs Fact Sheet If you are taking out a conforming loan today, you are almost certainly looking at a 5/6 ARM. The 5/1 structure still exists in portfolio loans and some non-conforming products, but the 5/6 has become the conventional-market standard.
With a 5/6 ARM, your rate can change twice a year during the adjustable phase. The rate caps on these loans account for the faster adjustment cycle, but the payment can still vary more often than under the old annual model.
How Your New Rate Is Calculated
When the adjustable phase begins, the lender does not pick a rate at will. Your new rate comes from a formula written into the loan contract, and it has two pieces.
The Index
The index is the variable piece. It reflects what is happening in the broader financial markets. Virtually all new ARMs today use the Secured Overnight Financing Rate, or SOFR, as their index. SOFR is based on actual overnight lending transactions backed by Treasury securities.2Freddie Mac. SOFR ARMs Fact Sheet Conforming ARM loans use the 30-day average of SOFR published by the Federal Reserve Bank of New York.
The Margin
The margin is the fixed piece. Your lender sets it when the loan is originated, and it never changes. If the 30-day average SOFR is 3.00% and your margin is 2.50%, your fully indexed rate is 5.50%. That is the rate the lender would charge for the next adjustment period, subject to the caps in your contract.
The Look-Back Period
Your lender does not use the index value from the day your rate resets. The contract specifies a look-back period, meaning the lender checks the index a set number of days before the adjustment date. For conforming loans, this is 45 days. If your rate adjusts on August 1, the lender uses the 30-day average SOFR from around June 17. The buffer gives the lender time to calculate your new rate and payment and send you the required notice before the change takes effect.
Rate Caps: The Built-In Guardrails
Rate caps prevent your interest rate from spiking without limit. Your contract defines three separate caps.
- The initial adjustment cap limits how much the rate can move at the first reset after the fixed period ends. On a typical 5-year SOFR ARM this is 2 percentage points, so a loan starting at 4.00% cannot exceed 6.00% at the first adjustment even if the fully indexed rate would be higher.
- The periodic adjustment cap limits how much the rate can change at each later reset. For conforming SOFR ARMs this is 1 percentage point per adjustment period, applied twice a year on a 5/6.2Freddie Mac. SOFR ARMs Fact Sheet
- The lifetime cap is the absolute ceiling for the loan. It is commonly 5 percentage points above your initial rate, so a loan starting at 4.00% could never exceed 9.00%.
These caps are often written in shorthand. A “2/1/5” cap structure means a 2-point initial cap, a 1-point periodic cap, and a 5-point lifetime cap. That is the standard structure for conforming 5-year ARMs.
The caps work in both directions. Periodic adjustment caps limit rate decreases as well as increases.3Fannie Mae. Adjustable-Rate Mortgages ARMs If SOFR drops sharply, your rate still cannot fall by more than the periodic cap at any single adjustment. Most loans also have a rate floor, often equal to the margin, meaning the rate will not drop below the lender’s markup no matter how low the index goes.1U.S. Department of Housing and Urban Development. FHA Adjustable Rate Mortgage
How the Monthly Payment Changes
When a new rate takes effect, your lender recalculates the monthly payment using three inputs: the adjusted interest rate, your remaining balance, and the number of months left on the loan. The new payment is set so the loan is fully paid off by the end of the original term. There is no balloon payment at the end, and standard ARMs do not allow negative amortization, where unpaid interest gets added to your balance.
The lender compares the fully indexed rate against the applicable cap and uses whichever is lower. If your fully indexed rate would be 6.50% but the initial cap limits you to 6.00%, you pay 6.00% until the next adjustment date.
The jump from a low introductory rate to a higher adjusted rate is what lenders call payment shock. Even with a 2-point initial cap, moving from a 4.00% rate to 6.00% on a $350,000 balance adds roughly $400 to the monthly principal and interest payment. On a 5/6 ARM, the six-month gap between adjustments gives you less time to absorb each change.
Payments can also fall. If market rates decline during the adjustable phase, your rate drops at the next reset (subject to the periodic cap and any floor), and the monthly payment follows.
Advance Notice Before Rate Changes
Federal law requires your lender to send you advance warning before any rate change. The timeline differs depending on whether it is the first adjustment or a later one.
For the initial rate adjustment at the end of the fixed period, the lender must send a disclosure between 210 and 240 days before the first payment at the new rate is due.4eCFR. 12 CFR 1026.20 – Disclosure Requirements Regarding Post-Consummation Events That is roughly seven to eight months of lead time, which gives you a real window to refinance or sell if you do not want to enter the adjustable phase.
For every adjustment after the first, the required notice window is shorter: at least 60 days and no more than 120 days before the first payment at the adjusted level is due.4eCFR. 12 CFR 1026.20 – Disclosure Requirements Regarding Post-Consummation Events
Each notice must include your current rate, the new rate, your current payment, the new payment amount, and an explanation of how the new rate was calculated, including the index value and margin used.5Consumer Financial Protection Bureau. 12 CFR 1026.20 – Disclosure Requirements Regarding Post-Consummation Events The notice also has to spell out your rate caps so you can see where your rate sits relative to the lifetime maximum.
No Prepayment Penalties
If you plan to refinance or pay off the loan before the adjustable phase begins, you will not face a prepayment penalty. Federal regulation prohibits prepayment penalties on any loan where the interest rate can increase after closing.6eCFR. 12 CFR 1026.43 – Minimum Standards for Transactions Secured by a Dwelling Every ARM by definition has a rate that can change, so prepayment penalties are off the table. You will still pay normal closing costs on a refinance, but the lender cannot charge a penalty for paying the loan off early.
When a 5-Year ARM Makes Sense
The core trade-off is straightforward: a lower rate now against uncertainty later. A 5-year ARM almost always starts with a lower interest rate than a 30-year fixed mortgage, and on a $400,000 loan the initial spread can be worth a few hundred dollars a month during the fixed period.
A 30-year fixed mortgage gives you the same payment from month one through the last month. You never need to plan an exit strategy, and the longer you hold the loan, the more that locked rate protects you against future increases. That predictability is worth paying for if you intend to stay in the home for a long time.
The 5-year ARM makes sense in a narrower set of situations. If you know you will sell the home within five years, you keep the savings and leave before any adjustment happens. If you expect rates to fall, the adjustable phase can work in your favor. And when the spread between fixed and adjustable rates is unusually wide, the early savings can be large enough to justify the risk.
Borrowers get into trouble in the middle case: they planned to sell or refinance before year five and could not. The housing market softened and they owe more than the home is worth. Their credit score dropped and they no longer qualify to refinance. Rates rose enough that refinancing into a fixed loan costs about the same as the adjusted ARM rate. Any of these can leave a borrower stuck in the adjustable phase without a workable exit. If your plan depends entirely on refinancing before the fixed period ends, work out what happens if that plan falls through before you sign.