ARMs: the worst case under the caps
An adjustable-rate mortgage (ARM) keeps its starting rate for a set time, then the rate can change on a schedule. Caps limit how far it can move. If you know your starting rate and caps, you can figure the highest rate, and the highest payment, the loan allows.
This is general education, not financial advice. This site doesn’t quote or predict rates or indexes. Your Loan Estimate and loan documents have your actual terms.
How an ARM rate is set
- After the starting period, the rate is the index plus the margin. The index is a measure of interest rates generally; the margin is an extra amount the lender adds.
- ARM names like 5/1 or 5/6m mean: the first number is how long the starting rate lasts, and the second is how often the rate can change after that. A 5/6m ARM keeps its rate for five years, then can adjust every six months. The time between changes is the adjustment period.Source: CFPB: “Adjustable-Rate Mortgages” booklet (Consumer Handbook on Adjustable-Rate Mortgages, last updated September 2026) · checked Nov 10, 2026
The three caps
- Initial adjustment cap: how much the rate can rise or fall the first time it adjusts, after the fixed period ends.
- Subsequent adjustment cap: how much it can rise or fall at each later adjustment, compared with the rate before it.
- Lifetime cap: how far it can ever move, in total, from the starting rate. Some loans also have a separate floor for decreases.Source: CFPB: “What are rate caps with an adjustable-rate mortgage (ARM), and how do they work?” (Ask CFPB #1951, last reviewed Jan 14, 2025) · checked Nov 10, 2026
Lenders sometimes write the caps as three numbers, such as 2/1/5: first change, each later change, and lifetime.Source: CFPB: “Adjustable-Rate Mortgages” booklet (Consumer Handbook on Adjustable-Rate Mortgages, last updated September 2026) · checked Nov 10, 2026 The caps are in percentage points added to the rate, not percent of the rate.
The worst-case path
Call the starting rate R, the caps first / later / lifetime. If the rate rises by the most the caps allow at every adjustment:
- During the fixed period: R.
- After the first adjustment: R + first (but not above R + lifetime).
- After each later adjustment: the previous rate + later, until it reaches R + lifetime.
- From then on: R + lifetime, the most the rate can ever be.
Each time the rate changes, the ARM worst-case calculator refigures the principal and interest payment so the remaining balance is paid off over the remaining term. That is how a fully amortizing ARM works; your note says how your own payment is set. Some ARMs have payment caps, interest-only periods, or negative amortization, which the calculator doesn’t model.Source: CFPB: “Adjustable-Rate Mortgages” booklet (Consumer Handbook on Adjustable-Rate Mortgages, last updated September 2026) · checked Nov 10, 2026
The CFPB suggests asking the lender to calculate the highest payment you may ever have to pay on the loan you’re considering.Source: CFPB: “What are rate caps with an adjustable-rate mortgage (ARM), and how do they work?” (Ask CFPB #1951, last reviewed Jan 14, 2025) · checked Nov 10, 2026
Where to find your numbers
- When you apply: for an ARM on your principal home with a term over one year, the lender must give you the Consumer Handbook on Adjustable Rate Mortgages (or a suitable substitute) and a loan program disclosure, when you get an application form or before you pay a non-refundable fee, whichever is earlier. The disclosure explains how the rate and payment are set, how often they change, and any rate or payment limits. It also includes either a historical example or the maximum rate and payment for a $10,000 loan assuming the maximum periodic increases.Source: 12 CFR 1026.19(b) (Regulation Z: disclosures for certain variable-rate transactions) · checked Nov 10, 2026
- Loan Estimate, Adjustable Interest Rate (AIR) table: index and margin, initial interest rate, minimum and maximum interest rate, when the rate may first change and how often after that, and the limits on the first change and on subsequent changes. The Closing Disclosure has the same table; see Loan Estimate vs. Closing Disclosure.
- Projected Payments table: the payment or range of payments over time. For an adjustable rate, the maximum principal and interest amounts are figured using the maximum possible interest rate.Source: 12 CFR 1026.37(c) and (j), and 1026.38(c) and (n) (Regulation Z: Projected Payments and Adjustable Interest Rate tables) · checked Nov 10, 2026
Notices before a change
- Before the first rate change, the lender or servicer must send a notice at least 210, but no more than 240, days before the first payment at the new level is due. If the new rate isn’t known yet, the notice shows an estimate, labeled as one.
- For later changes that change the payment, the notice generally comes at least 60, but no more than 120, days before the first new payment is due. Some loans have shorter timing.Source: 12 CFR 1026.20(c) and (d) (Regulation Z: ARM rate adjustment notices) · checked Nov 10, 2026
Program rules
| Program | Rule | Source |
|---|---|---|
| FHA | Fixed periods of 1, 3, 5, 7, or 10 years, then the rate may change annually. 1- and 3-year ARMs: up 1 point a year, 5 over the life of the loan. 5-year: 1 and 5, or 2 and 6. 7- and 10-year: 2 a year, 6 over the life of the loan. Index: 1-year Constant Maturity Treasury or 30-day average SOFR. The loan must be fully amortizing over no more than 30 years. | Source: HUD Handbook 4000.1, II.A.8 (Section 251 adjustable rate mortgages) · checked Nov 10, 2026 |
| Conventional: Fannie Mae | The rate used for the payment in the debt-to-income ratio depends on the fixed period: 3 years or less, the highest rate possible in the first 5 years; 5 years, the greater of the note rate plus the first change cap or the fully indexed rate; longer, no less than the note rate. | Source: Fannie Mae Selling Guide B3-6-04, Qualifying Payment Requirements · checked Nov 10, 2026 |
| VA | The statutes: a traditional ARM’s rate changes once a year, by no more than 1 percentage point at a change and 5 points over the life of the loan (38 U.S.C. 3707). A hybrid ARM’s starting rate is fixed for at least the first 3 years, then changes once a year, with the caps left to VA (38 U.S.C. 3707A).Source: 38 U.S.C. 3707, Adjustable rate mortgages (U.S. Code, 2024 edition); 38 U.S.C. 3707A, Hybrid adjustable rate mortgages (U.S. Code, 2024 edition) · checked Nov 10, 2026 The regulation, 38 CFR 36.4312(d): rate changes happen once a year, and the first can come no sooner than 36 months after the first payment. No single change can move the rate more than 1 percentage point up or down, and changes over the life of the loan can’t move it more than 5 points from the starting rate. The index it names is the weekly average yield on 1-year Treasury bills adjusted to a constant maturity.Source: 38 CFR 36.4312(d) (VA adjustable rate mortgage requirements; last amended 2015) · checked Nov 10, 2026 VA’s handbook, hybrid ARMs (Chapter 7, Topic 6): if the rate is fixed for less than 5 years, the first change is limited to 1 point and the lifetime increase to 5 points; if it is fixed 5 years or more, the first change is limited to 2 points and the lifetime increase to 6 points.Source: VA Pamphlet 26-7, Lenders Handbook, Chapter 7, Topic 6, Adjustable-Rate Mortgages (change date Mar 11, 2019; KnowVA article updated Jul 24, 2026) · checked Nov 10, 2026 For the payment used in underwriting, the handbook says an ARM that can change after 1 year is figured at 1 point above the starting rate, and a hybrid with a fixed period of 3 years or more may be figured at the starting rate.Source: VA Pamphlet 26-7, Lenders Handbook, Chapter 7, Topic 6, Adjustable-Rate Mortgages (change date Mar 11, 2019; KnowVA article updated Jul 24, 2026) · checked Nov 10, 2026 | Checked against the statute, regulation, and handbook |
| Conventional: Freddie Mac | Products: 3/6-, 5/6-, 7/6-, and 10/6-month ARMs, fixed for 36, 60, 84, or 120 months, then the rate changes every 6 months. Only ARMs using the 30-day Average SOFR index are eligible. The margin is 100 to 300 basis points (1 to 3 percentage points). Each later change is capped at 1 percentage point and the lifetime increase at 5 points. The first change is capped at 2 points for 3/6 and 5/6 ARMs and 5 points for 7/6 and 10/6 ARMs. The rate can’t go below the margin.Source: Freddie Mac Single-Family Seller/Servicer Guide, Section 4401.1, General ARM eligibility requirements (effective 11/05/2025) · checked Nov 10, 2026 Rate used for the payment in the debt-to-income ratio: 3/6, the note rate plus the life cap; 5/6, the greater of the note rate plus 2 percentage points or the fully indexed rate; 7/6 and 10/6, the note rate, or for higher-priced loans (HPML/HPCT) the greater of the note rate or the fully indexed rate. For 3/6 and 5/6 ARMs, the starting rate can’t be more than 3 percentage points below the fully indexed rate.Source: Freddie Mac Single-Family Seller/Servicer Guide, Section 4401.2, Underwriting requirements for ARMs (effective 07/02/2025) · checked Nov 10, 2026 | Checked in a browser (the Guide blocks automated reads) |
| USDA | Not available. A USDA guaranteed loan must have a rate that is fixed over the term of the loan, and adjustable-rate mortgages are listed as ineligible terms.Source: 7 CFR 3555.104(a)–(b) (USDA guaranteed loan terms) · checked Nov 10, 2026 | Checked against the regulation |
Lenders can set their own ARM terms within these rules. See your own figures in the ARM worst-case calculator.
Guidelines change; confirm with a licensed lender.