A 3/27 adjustable-rate mortgage (ARM) is a 30-year mortgage with a rate fixed for the first three years and an adjustable rate for the remaining 27 years.
The notation is easy to misread. The 27 is the length of the remaining adjustable period. The 27 does not mean the rate adjusts once every 27 years.
The 27 is a remaining term, not a reset interval
Months 1 through 36 use the loan's initial fixed rate. After that, the loan enters its adjustable period.
A 3/1 ARM uses its second number to communicate a typical reset interval. A 3/27 ARM uses the second number differently: it identifies the 27 years left in the 30-year term.
Historical 3/27 loans often used six-month adjustment intervals after the initial period, but the shorthand alone does not establish the schedule. The Consumer Financial Protection Bureau emphasizes reading the actual ARM terms; the note, ARM rider, and servicing disclosures control.
The reset rate is a contract calculation
An ARM generally combines a benchmark index with a lender-set margin:
1fully indexed rate = index + marginContractual rate caps can limit the rate applied at the first adjustment, later adjustments, or over the life of the loan.
That creates four separate inputs to inspect:
- the index or replacement benchmark;
- the margin;
- the timing of each reset; and
- the initial, periodic, and lifetime caps.
Historical indexes such as the 11th District Cost of Funds Index help explain older ARM documents, but the governing contract determines the actual benchmark and fallback mechanics for a particular loan.
Payment shock is a cash-flow problem, not just a rate quote
The first reset matters because a higher rate can raise the required payment after three years of lower fixed payments.
The size of that change depends on more than the new interest rate. Remaining principal, remaining amortization term, cap structure, and any unusual payment provisions also matter.
A borrower who expects to refinance before the first reset still carries refinancing risk. Property values, credit conditions, underwriting standards, or personal finances can change before month 37.
Collateral leverage is a separate axis
ARM reset risk should not be confused with negative equity.
A 125% loan describes debt relative to collateral value. A 3/27 ARM describes how the interest rate changes over time. One loan can have either risk, both risks, or neither.
That distinction is especially important when reading pre-2008 mortgage records, where product structure, borrower equity, introductory pricing, and underwriting quality can otherwise get collapsed into one label.
Read the loan documents in the order cash flows change
For an older 3/27 ARM, the most useful sequence is:
- identify the initial fixed rate and its end date;
- identify the first adjustment date and later reset frequency;
- find the index, margin, and any replacement-benchmark provision;
- apply the first, periodic, and lifetime caps; and
- translate the permitted rate into the required payment under the remaining amortization schedule.
That workflow turns the product name into the cash-flow mechanics that actually affect the borrower.
Primary sources
- CFPB Consumer Handbook on Adjustable-Rate Mortgages
- CFPB: What to look for in an ARM
- CFPB: ARM index and margin
- CFPB: ARM rate caps
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