3/1 ARM Calculator
See the initial payment on a 3/1 adjustable-rate mortgage — fixed for 3 years, then adjusting annually — and the payment shock once it resets.
How the 3/1 arm calculator works
A 3/1 ARM holds your rate for just three years, then adjusts annually for the rest of the term. This tool amortizes the loan at the low start rate across those three years, then recomputes the payment at your estimated post-adjustment rate over the remaining months.
Three years is the shortest common fixed window, so it usually carries the lowest start rate of the group but the soonest reset risk, well ahead of a 5/1, 7/1, or 10/1. At each adjustment the rate becomes the index, typically SOFR, plus your fixed margin, held within the initial, periodic, and lifetime caps. The tool shows the opening payment, the payment after the first reset, and the balance owed at the three-year mark.
Worked example: with loan amount of $425,000, loan term (years) of 30 and initial fixed rate (3 yrs) of 5.75%, the 3/1 arm calculator shows initial monthly payment of $2,480.18.
- Payment (first 3 yrs)
- $2,480.18
- Payment after reset
- $2,937.79
- Balance at reset
- $407,611
- Rate change
- 5.75% → 7.50%
| Loan amount | Initial monthly payment |
|---|---|
| $300,000 | $1,750.72 |
| $425,000 | $2,480.18 |
| $550,000 | $3,209.65 |
| $700,000 | $4,085.01 |
The formula
The initial payment amortizes the full balance at the start rate over the whole term. After three years the adjusted rate equals index + margin, capped first by the initial cap and then by periodic and lifetime caps. The balance remaining at year three re-amortizes at that capped rate across the months still left.
- The rate is fixed for three years and then adjusts every year, the structure that defines a 3/1 ARM.
- Caps are interpreted as initial/periodic/lifetime, so a 2/2/6 set bounds the first move, later moves, and the lifetime rise above the start rate.
- The estimated adjusted rate is your own input; future index levels three years out cannot be forecast by any tool.
- The margin is locked for the loan's life and added to the index value applying at each annual reset.
- Escrowed taxes and insurance, plus HOA dues and closing costs, fall outside the principal-and-interest figures here.
Results are estimates for educational purposes and are not financial advice. Confirm exact figures with your lender or a licensed advisor.
Questions about the 3/1 arm calculator
When does a 3/1 ARM make sense over a 5/1?
Only when your horizon is genuinely short, roughly three years or less. The 3/1 trades two years of certainty for a slightly lower start rate, which rarely justifies the earlier reset unless you are confident you will sell or refinance before year three.
For most buyers the extra certainty of a 5/1 is worth its modest premium.
How quickly can my payment change on a 3/1 ARM?
Your first adjustment lands at the start of year four, and after that the rate can move every twelve months. That is the soonest and most frequent reset schedule among the common ARMs.
The initial cap limits the first jump and the periodic cap limits each yearly move, but you face rate uncertainty far earlier than with longer-fixed ARMs.
Is the lower start rate on a 3/1 worth the early reset risk?
It depends entirely on timing. If you exit before the three-year mark, the discount is pure savings with no reset exposure.
If you hold longer, the shorter fixed period means you start absorbing annual rate risk sooner than any other ARM, and a rising index can erase the early savings quickly. Match the loan to a firm exit plan.
Is the 3/1 ARM Calculator free to use?
Yes. Every calculator on MortgageLoansCalculator is completely free, with no sign-up, login or paywall. Run as many scenarios as you like.
What is a 3/1 ARM?
A 3/1 ARM is fixed for three years, then adjusts annually. It offers the lowest starting rate of the common ARMs but the shortest protection, so it fits only borrowers confident they will move or refinance within a few years.
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