A fixed-rate loan is easy to explain: the rate on day one is the rate on the last day. An adjustable-rate mortgage (ARM) is where the SAFE exam gets to test vocabulary, math, and disclosure law in a single question. ARMs sit in General Mortgage Knowledge, which is 20% of the national SAFE MLO test, but the disclosure rules behind them belong to Federal Mortgage-Related Laws (24%), and the caps math can show up anywhere.
This guide walks through how an ARM is built, how to read the names and the cap numbers, the features that create payment shock, and the Regulation Z disclosures a borrower must get before and after closing.
How an ARM rate is built
Every ARM rate after the first adjustment comes from two pieces:
- The index is a published market rate the lender does not control. It moves up and down over the life of the loan.
- The margin is a fixed number of percentage points the lender adds to the index. It is set in the note and does not change for the life of the loan.
Index plus margin equals the fully indexed rate. If the index is 4.25% and the margin is 2.75%, the fully indexed rate is 7.00%. The caps in the note then decide whether the borrower actually pays that rate at a given adjustment.
The exam often asks which part can change. The answer is the index. If a question says the margin went up at the second adjustment, something is wrong with that answer choice.
Common indexes
Most new ARMs today use the Secured Overnight Financing Rate (SOFR), usually as a 30-day average, which is published by the Federal Reserve Bank of New York. You may also see the one-year Constant Maturity Treasury (CMT) index. LIBOR was the most common ARM index for years, but U.S. dollar LIBOR stopped being published after June 30, 2023, and loans tied to it were moved to a replacement index. On the exam, know that the index must be outside the lender’s control and that the borrower is told where to find it.
Lookback and rounding
The note says which index value to use. A common choice is the most recent value available 45 days before the change date, called the lookback period. Many notes also round the result to the nearest one-eighth of a point (0.125%). A fully indexed rate of 7.40% would round to 7.375%.
Reading ARM names
A hybrid ARM has a fixed rate for an initial period, then adjusts. The name tells you both numbers:
- 5/1 ARM: fixed for 5 years, then adjusts once a year.
- 7/1 ARM: fixed for 7 years, then adjusts once a year.
- 5/6 ARM: fixed for 5 years, then adjusts every 6 months. The “6” is months, not years. This style is common with SOFR loans.
- 1-year ARM: adjusts every year from the start.
The first number is always the length of the initial fixed period in years. The second number is how often the rate changes after that. A test question that calls a 5/1 ARM “a loan that adjusts every five years” is a trap.
Other terms to know:
- Change date: the date the new rate takes effect.
- Adjustment period: the time between rate changes.
- Initial rate (start rate): the rate during the fixed period.
- Discounted or teaser rate: an initial rate set below the fully indexed rate at closing. A discounted start rate almost guarantees the rate will rise at the first change date, even if the index stays flat.
Rate caps
Caps protect the borrower by limiting how far the rate can move. There are three kinds, and the exam writes them as three numbers in this order:
| Position | Cap | What it limits |
|---|---|---|
| First | Initial adjustment cap | The change at the first change date |
| Second | Periodic (subsequent) cap | The change at each later change date |
| Third | Lifetime cap | How far the rate can ever rise above the initial rate |
So 2/1/5 means the rate can move up to 2 points at the first adjustment, up to 1 point at each adjustment after that, and never more than 5 points above the start rate. The lifetime cap is measured from the initial rate, not from the fully indexed rate and not from the previous rate.
In many notes the periodic caps work in both directions, so they also limit how fast the rate can fall. Many notes also set a floor, a minimum rate the loan can never go below, which is often equal to the margin.
Worked example
A 5/6 ARM starts at 6.00% with a 3.00% margin and 2/1/5 caps. The note rounds to the nearest one-eighth of a point.
- Lifetime maximum: 6.00% + 5 = 11.00%.
- First change date (after five years): the index is 4.40%, so the fully indexed rate is 7.40%, rounded to 7.375%. The first-adjustment cap allows up to 8.00%, so the new rate is 7.375%.
- Second change date (6 months later): the index is 5.60%, so the fully indexed rate is 8.60%, rounded to 8.625%. The periodic cap allows only 1 point over 7.375%, so the new rate is 8.375%.
The order of operations is the whole question: build the fully indexed rate, then apply the cap that fits this adjustment, then check the lifetime cap. If a cap holds the rate below the fully indexed rate, some notes allow interest rate carryover, meaning the increase that was not applied can be added at a later adjustment. The ARM program disclosure must say whether carryover applies.
Payment caps and negative amortization
A payment cap limits how much the monthly payment can change, often by a percentage, instead of limiting the rate. That sounds friendly, but it creates a gap. If the rate rises and the capped payment no longer covers the interest due, the unpaid interest is added to the loan balance. That is negative amortization: the borrower makes every payment and still owes more than before.
Loans with negative amortization usually have a recast point, when the balance reaches a set limit or a set date arrives, and the payment is reset to fully amortize the loan over the remaining term. That reset can be a large jump. The older “option ARM,” which let the borrower choose a minimum payment below the interest due, worked this way and was a major source of payment shock before 2008.
Know the regulatory consequence: a qualified mortgage cannot have negative amortization, interest-only payments, or a term over 30 years, and HOEPA high-cost mortgages also ban negative amortization. A loan with these features can still be made, but it is not a QM.
Other ARM features
- Interest-only ARM: the borrower pays only interest for a set period, often the fixed period. When that ends, the payment jumps to cover principal over the shorter remaining term, on top of any rate change.
- Convertible ARM: the note lets the borrower switch to a fixed rate during a set window, usually for a fee. The new fixed rate follows a formula in the note.
- Payment shock: the general term for a sharp payment increase after an adjustment, a recast, or the end of an interest-only period. Expect it in both knowledge questions and ethics scenarios about explaining risk to a borrower.
Underwriting an ARM
The ability-to-repay rule in Regulation Z keeps a lender from qualifying a borrower on the teaser payment alone. Under the general rule, the payment is figured using the greater of the fully indexed rate or the introductory rate, with monthly, fully amortizing payments. For a qualified mortgage, an ARM is underwritten using the maximum rate that can apply during the first five years after the first regular payment is due. The ATR and QM guide covers the rest of those rules.
Disclosures before closing
The early ARM disclosures
Regulation Z section 1026.19(b) applies when the APR may increase after consummation on a loan secured by the consumer’s principal dwelling with a term greater than one year. The borrower gets two things:
- The CHARM booklet, the Consumer Handbook on Adjustable-Rate Mortgages, or a suitable substitute.
- A loan program disclosure for each ARM program the consumer is interested in. It explains that the rate, payment, or term can change, names the index and where to find it, explains how the rate is figured (index plus margin), states the frequency of changes, describes any caps, negative amortization, or carryover, and gives either a historical example based on a $10,000 loan or the maximum rate and payment on a $10,000 loan.
Timing is the tested detail: these go out when an application form is provided or before the consumer pays a non-refundable fee, whichever is earlier. If the application comes in by phone or through a broker, they may be delivered or mailed within three business days of receiving it.
On the Loan Estimate and Closing Disclosure
For an ARM, the Loan Terms table answers “Yes” to whether the interest rate and the monthly payment can increase after closing, with details. The Projected Payments table shows payment ranges for the years when the rate can change. Page 2 of the Loan Estimate, and the matching page of the Closing Disclosure, includes the Adjustable Interest Rate (AIR) table: index and margin, initial rate, minimum and maximum rate, how often the rate changes (first change and subsequent changes), and the limits on each change. A loan whose payment can change for other reasons, such as an interest-only period, also gets an Adjustable Payment (AP) table. The TRID guide covers the timing of those forms.
Advertising
Under TILA’s advertising rules, an ad that states an APR for a loan where that rate may increase after consummation must say so. A low starting rate cannot be shown as if it were the rate for the life of the loan.
Notices after closing
Section 1026.20 adds two notices for closed-end ARMs secured by the consumer’s principal dwelling. Both come from the creditor, assignee, or servicer, and ARMs with terms of one year or less are exempt.
| Notice | When it is due |
|---|---|
| Initial rate adjustment, 1026.20(d) | At least 210 but no more than 240 days before the first payment at the new rate is due. If that payment is due within 210 days after consummation, it is given at consummation. |
| Rate change with a payment change, 1026.20(c) | At least 60 but no more than 120 days before the first payment at the new level is due. A shorter 25 to 120 day window applies to ARMs that adjust every 60 days or more often and to certain older loans. |
The initial adjustment notice must be a separate document. If the new rate is not yet known, it gives an estimate and labels it as one.
How the exam tests ARMs
- Index versus margin. The index moves; the margin is fixed for the life of the loan.
- Lifetime cap math. Add the lifetime cap to the initial rate, not to the fully indexed rate.
- Which cap applies. The first number applies once, at the first change date. Every later change uses the second number.
- The 5/6 name. Five years fixed, then changes every six months.
- Teaser rates. A discounted start rate means the payment will likely rise even if the index does not.
- Negative amortization. Caused by a payment cap or minimum payment that does not cover interest, and it disqualifies a loan from QM status.
- CHARM timing. At application or before a non-refundable fee, whichever is earlier, for principal-dwelling ARMs over one year.
- 210 to 240 days for the first adjustment notice; 60 to 120 days for later payment changes.
Quick review
- Fully indexed rate = index + margin, then limited by the caps.
- Most new ARMs use SOFR; LIBOR ended after June 30, 2023.
- 5/1 adjusts yearly after five years; 5/6 adjusts every six months after five years.
- Caps read initial / periodic / lifetime, and the lifetime cap is measured from the start rate.
- Payment caps can cause negative amortization; QMs cannot have it.
- ATR underwriting uses the greater of the fully indexed or introductory rate; QM uses the highest rate possible in the first five years.
- Before closing: CHARM booklet and program disclosure, then the AIR table on the Loan Estimate and Closing Disclosure.
- After closing: the initial adjustment notice and payment change notices under 1026.20.
Practice this on MLO Pass
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Related study guides
- NMLS Exam Math: Mortgage Formulas and Worked Examples
- Ability-to-Repay and Qualified Mortgages: ATR/QM on the SAFE Exam
- TRID Made Simple: Loan Estimate & Closing Disclosure Timelines
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