Adjustable-Rate Mortgage Calculator
3/1 ARM Calculator
Estimate your 3/1 ARM payment during the first three years, then model annual rate resets using index + margin and the cap structure from your loan offer. See the projected first adjusted payment, long-term payment path, and a cap-based stress test.
Last reviewed: September 1, 2026
3/1 ARM Mortgage Calculator
Estimate the first 3 years, annual resets after month 36, and a cap-based payment stress test.
3/1 ARM Loan Details
Your 3/1 ARM Results
Includes principal and interest at the initial ARM rate plus entered property taxes, homeowners insurance, HOA fees, and estimated PMI when applicable.
Under the projected rate path, estimated interest through year 7 is $176,287, with about $329,764 remaining on the loan. The modeled P&I payment at that horizon is about $2,724 per month.
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| Month | Target Rate | Capped Rate | New P&I | Balance |
|---|---|---|---|---|
| 37 | 7.750% | 7.750% | $2,555 | $346,196 |
| 49 | 8.000% | 8.000% | $2,612 | $342,238 |
| 61 | 8.250% | 8.250% | $2,669 | $338,133 |
| 73 | 8.500% | 8.500% | $2,724 | $333,859 |
| 85 | 8.750% | 8.750% | $2,779 | $329,390 |
| 97 | 9.000% | 9.000% | $2,832 | $324,696 |
| 109 | 9.250% | 9.250% | $2,884 | $319,746 |
| 121 | 9.500% | 9.500% | $2,936 | $314,504 |
| 133 | 9.750% | 9.750% | $2,986 | $308,929 |
| 145 | 10.000% | 10.000% | $3,034 | $302,974 |
| 157 | 10.250% | 10.250% | $3,082 | $296,586 |
| 169 | 10.500% | 10.500% | $3,127 | $289,705 |
| 181 | 10.750% | 10.750% | $3,171 | $282,261 |
| 193 | 11.000% | 11.000% | $3,213 | $274,174 |
| 205 | 11.250% | 11.250% | $3,254 | $265,351 |
| 217 | 11.500% | 11.250% | $3,254 | $255,670 |
| 229 | 11.750% | 11.250% | $3,254 | $244,842 |
| 241 | 12.000% | 11.250% | $3,254 | $232,731 |
| 253 | 12.250% | 11.250% | $3,254 | $219,184 |
| 265 | 12.500% | 11.250% | $3,254 | $204,033 |
| 277 | 12.750% | 11.250% | $3,254 | $187,087 |
| 289 | 13.000% | 11.250% | $3,254 | $168,133 |
| 301 | 13.250% | 11.250% | $3,254 | $146,933 |
| 313 | 13.500% | 11.250% | $3,254 | $123,221 |
| 325 | 13.750% | 11.250% | $3,254 | $96,699 |
| 337 | 14.000% | 11.250% | $3,254 | $67,035 |
| 349 | 14.250% | 11.250% | $3,254 | $33,856 |
Important 3/1 ARM Assumptions
This calculator assumes a three-year initial fixed period and annual adjustments afterward. It models future rates from the index, margin, index-change assumption, and caps you enter. It does not forecast an ARM index. Actual loan documents may include floors, rounding rules, different cap definitions, and other provisions that change the result.
Compare 3/1 ARM Rates
Compare Current 3/1 ARM Mortgage Offers
Review available 3-year ARM offers from participating lenders after modeling how the payment may change after the initial fixed period.
What is a 3/1 ARM?
A 3/1 ARM is an adjustable-rate mortgage that generally keeps its initial interest rate for the first three years and then adjusts once per year. The starting rate and principal-and-interest payment are therefore predictable for the first 36 months, while later payments depend on the loan's adjustment formula and caps.
Because the first reset arrives relatively early compared with a 5/1, 7/1, or 10/1 ARM, understanding the post-reset payment is especially important when evaluating a 3/1 ARM.
How a 3/1 ARM rate changes after year 3
Many ARMs determine the new rate from a benchmark index plus a lender margin. The result is the fully indexed rate, but the mortgage's caps can limit how far the actual rate changes at each reset.
Target rate = index + margin
The calculator then applies the first-adjustment, periodic, and lifetime caps entered for your 3/1 ARM.
The first reset is the key 3/1 ARM decision point
A 3/1 ARM's first adjustment generally occurs after the first 36 scheduled payments. That means the rate can begin changing in year four. If you expect to keep the mortgage beyond three years, the first-reset payment and later annual cap structure deserve as much attention as the introductory rate.
The calculator therefore emphasizes the initial payment, first adjusted rate, first adjusted payment, and a separate cap-stress scenario rather than showing only a long-term interest total.
Understanding 3/1 ARM caps
First adjustment cap
Limits how much the rate can move at the first reset after the three-year introductory period.
Periodic cap
Limits how much the rate can change at each later annual adjustment.
Lifetime cap
Limits how far the rate can rise above the original ARM rate over the life of the loan.
Cap notation and definitions can vary between products and lenders. Use the terms shown in the lender's ARM disclosures rather than assuming every 3/1 mortgage follows the same limits.
What is the 3/1 ARM payment stress test?
The stress test assumes the rate rises by the maximum amount allowed by the first-adjustment cap and each later periodic cap until the lifetime ceiling is reached. It gives you a conservative payment path for testing affordability if rates move against you.
It is not a forecast. Actual rates may rise, fall, or remain relatively stable depending on the index, margin, caps, floors, and market conditions.
When a 3/1 ARM may be worth considering
A 3/1 ARM may be worth comparing when its introductory pricing is materially lower than available fixed-rate options and your expected time in the mortgage is short. For example, a borrower who reasonably expects to sell before the first adjustment may place more weight on the initial three-year period.
That expected exit should not be treated as guaranteed. If a sale or refinance does not happen, the borrower remains exposed to the annual adjustment rules after year three.
3/1 ARM vs. 5/1, 7/1 and fixed-rate mortgages
A 3/1 ARM begins adjusting sooner than longer introductory ARM structures. A 5/1 or 7/1 ARM generally provides a longer initial fixed period, while a fixed-rate mortgage keeps the same rate for the full term.
If your main question is whether an adjustable or fixed mortgage is better for your situation, use the ARM vs. Fixed Mortgage Calculator. For a broader adjustable-rate analysis, use the ARM Mortgage Calculator.
Frequently asked questions
When does a 3/1 ARM first adjust?
A typical 3/1 ARM keeps the introductory rate for three years and first adjusts after that fixed period, generally beginning with the payment period after month 36. Verify the dates in the specific loan documents.
How often does a 3/1 ARM adjust after year 3?
The /1 generally indicates annual adjustments after the initial three-year fixed period.
Can a 3/1 ARM rate go down?
Potentially. If the underlying index declines, the fully indexed rate may be lower at a reset. Caps, floors, the margin, and other contract provisions can affect the actual rate.
Is a 3/1 ARM risky?
Its main risk is payment uncertainty beginning relatively soon after origination. The significance of that risk depends on the starting-rate advantage, cap structure, future index values, and how long you expect to keep the loan.
Can I refinance before the first 3/1 ARM reset?
Potentially, but refinancing is not guaranteed. Future rates, home value, credit, income, closing costs, and underwriting requirements can all affect whether refinancing is available or worthwhile.
What should I compare besides the initial 3/1 ARM rate?
Review the margin, index, first and later adjustment caps, lifetime cap, floors, points, lender fees, maximum payment information, and how long you expect to keep the mortgage.
Methodology and related ARM calculators
MortgagePaymentCalculator.io is published by Family Brands LLC. Calculator results are estimates for educational and planning purposes and are not mortgage offers, approvals, rate forecasts, or lender disclosures.