ARM vs Fixed: What Is a 5/6 ARM and When Does It Make Sense?

A fixed-rate mortgage keeps the same interest rate for the entire loan, while an adjustable-rate mortgage (ARM) starts with a lower introductory rate for a set period and then adjusts periodically after that. The most common ARM today is the 5/6 ARM, which carries its introductory rate for the first five years and then adjusts every six months for the rest of the loan.

An ARM can save you money up front, but only if you understand exactly when and how the rate changes. The single biggest mistake buyers make is assuming the introductory rate is locked for the whole loan, or even that they are safe because someone told them it is "fixed for five years." Here is how these loans actually work and who they fit.

Rate structures described reflect standard ARM products as of July 2026. Specific terms vary by lender and program.

What is the difference between a fixed and adjustable-rate mortgage?

A fixed-rate mortgage locks your interest rate and principal-and-interest payment for the life of the loan, whether that is 15 or 30 years. It never changes, which makes budgeting simple and protects you if rates rise.

An adjustable-rate mortgage starts with a lower rate during an introductory period, then adjusts up or down based on a market index plus a set margin. You trade the certainty of a fixed rate for a lower starting payment, and you take on the risk that your rate and payment can rise once the introductory period ends. Which one is better depends entirely on how long you plan to keep the loan and how much rate risk you can absorb. It is worth checking where today's mortgage rates sit before you decide, since the gap between fixed and ARM pricing drives the whole calculation.

What is a 5/6 ARM?

A 5/6 ARM is an adjustable-rate mortgage where the introductory rate applies for the first five years, and then the rate adjusts every six months for the remaining loan term. The two numbers tell you the structure: the 5 is the length of the introductory period in years, and the 6 is how often, in months, the rate adjusts after that.

You may also see the older 5/1 ARM, where the rate adjusted once a year after the initial period. Most current ARMs have moved to the 5/6 structure, adjusting every six months rather than annually, because the index they are tied to changed. When people search for a "5/1 ARM," what they can actually get today is usually a 5/6 ARM. Both share the same idea: a five-year introductory period followed by regular adjustments.

Is a 5/6 ARM fixed for the first five years?

This is where careful language matters, and where a lot of borrowers get misled. It is accurate to say the introductory rate applies for the first five years, but it is misleading, and actually a violation of federal advertising rules, to call the loan "fixed for five years" without also stating that the rate adjusts and the payment can increase after that period.

Federal Regulation Z, at 12 CFR 1026.24, specifically prohibits using the word "fixed" to describe an ARM's introductory period unless the ad clearly identifies the loan as an ARM and states, with equal prominence, the exact time period the rate holds and the fact that it can change afterward. So any lender who tells you a 5/6 ARM is simply "fixed for five years" is either being sloppy or cutting a corner they are not allowed to cut. The honest way to say it is this: the rate is set for an introductory five-year period, and then it begins adjusting every six months, which means your payment can rise. I point this out because how a lender describes an ARM tells you something about how carefully they follow the rules, and you want to work with one who gets it right. I am Emmett Clark, a mortgage broker licensed in 18 states with more than 20 years of experience.

How much can the rate go up on an ARM?

ARMs have built-in caps that limit how much the rate can rise, and understanding them is essential before you take one. There are typically three caps: an initial adjustment cap, a periodic cap, and a lifetime cap.

The initial cap limits how much the rate can jump at the very first adjustment after the introductory period. The periodic cap limits each adjustment after that. The lifetime cap sets the absolute ceiling over the life of the loan. For example, caps written as 2/1/5 would mean the rate can rise up to 2% at the first adjustment, up to 1% at each following adjustment, and no more than 5% above your start rate ever. These caps are your protection, and you should know all three numbers before you sign, because they define your worst-case payment. You can run both the intro and worst-case payments in a calculator to see the full range before you commit.

When does an ARM make sense?

An ARM makes the most sense when you are confident you will sell or refinance before the introductory period ends. If you know you will move within five years, or you fully expect to refinance, the lower introductory rate on a 5/6 ARM can save you real money during the years you actually hold the loan, and the later adjustments may never affect you.

A fixed rate makes more sense when you plan to stay long term, when you want payment certainty, or when rates are low enough that locking one in is clearly worth it. If certainty is your priority, a standard fixed-rate conventional loan may be the better fit. The risk with an ARM is always that your plans change, you keep the loan longer than expected, and you face higher payments when rates rise. Because that risk is real, an ARM should be a deliberate choice matched to a clear plan, not a way to squeeze into a house you cannot otherwise afford. With access to both fixed and adjustable products across 240-plus wholesale lenders, I can run the actual numbers both ways and show you the break-even point for your situation. For more foundational guides like this one, see our mortgage basics guide.