Arm Vs Fixed Mortgage Calculator

An adjustable-rate mortgage tempts you with a lower starting rate, then changes the deal after a few years. The only question that matters: will you sell, refinance, or pay it off before the higher payments erase the early savings? This ARM vs fixed mortgage calculator runs both 30-year loans side by side on the same loan amount, finds the break-even year when the ARM’s cumulative payments catch up, and shows the worst-case monthly payment at your lifetime rate cap.

Quick Answer

How to use the ARM vs fixed calculator

Enter one loan amount and the two offers in front of you, then compare. Both sides of the comparison are 30-year loans; the term is not an input.

1. Loan amount and fixed rate: the amount after your down payment, and the 30-year fixed quote you could lock today. That fixed payment is the baseline everything is measured against.
2. ARM initial rate and fixed period: the ARM’s starting rate and how long it lasts: 5 years for a 5/1, 7 for a 7/1, 10 for a 10/1.
3. Rate after adjustment: your scenario for where the rate lands at the first reset. The model adjusts once to this rate and holds it, so treat it as the scenario you want to test: today’s fully indexed rate for a neutral case, a higher number for a stress test.
4. Lifetime rate cap: enter the maximum rate itself, not the points above the start. A 5.25% start with a 5-point lifetime cap is entered as 10.25. The cap feeds the worst-case payment figure; it does not restrain the scenario rate in the simulation.
5. Years you plan to hold: your honest exit horizon. The verdict badge compares it with the break-even year, and the breakdown shows how much cheaper or costlier the ARM is over exactly that hold.

The pre-filled example is the one used throughout this page: $320,000, fixed 6.5%, 5/1 ARM at 5.25%, scenario 7.5%, cap 10.25%, 10-year hold. Change any field and the story changes with it: a 7/1 at a smaller discount, or a scenario rate at the cap, produces a different break-even and often a different winner. For the plain fixed-rate baseline on its own, run the same amount through the mortgage payment calculator.

How the comparison actually works

Both loans are simulated month by month for 30 years. The ARM’s balance is re-amortised once, at the end of its fixed period, over the remaining term at your scenario rate, and break-even is the first month the ARM’s cumulative payments overtake the fixed loan’s.

Three mechanics are worth knowing before you quote the break-even year to anyone. First, the post-reset payment is computed on the balance that remains when the fixed period ends, spread over the years left: that is why the 7.5% payment is $2,179 and not the $2,237 a fresh $320,000 loan at 7.5% would carry. Second, the banked figure is the unrounded payment difference ($255.57) multiplied by the 60 months, with no interest earned on the savings. Third, the verdict follows your hold input, not the break-even alone: at a 20-year hold the badge flips to the fixed loan, because by then the ARM has cost $12,837 more in payments.

Caps are the whole risk story

An ARM’s rate after the fixed period is the index (today usually SOFR) plus the lender’s margin, but three caps bound it: the initial cap on the first adjustment, the periodic cap on each later adjustment, and the lifetime cap, the absolute maximum. The Consumer Financial Protection Bureau’s explanation of mortgage rate caps walks through the same three limits, and its adjustable-rate mortgage overview is the plainest official summary of how the pieces fit.

A 2/2/5 structure on a 5.25% start means at most 7.25% after the first adjustment and 10.25% ever, which is exactly the cap entered in the worked example. Two cautions follow. The cap you type here is the ceiling rate itself, so a lender quoting “5% lifetime” on a 6% start means an 11% entry, not 5. And the cap restrains a real ARM gradually, adjustment by adjustment, while this model jumps straight to your scenario rate: if your scenario is above the first-adjustment cap, a real loan would take longer to get there than the simulation assumes. Federal rules also work in your favour on timing: under Regulation Z, your servicer must send the first adjustment notice 210 to 240 days before the first payment at the adjusted rate is due, per the CFPB’s Regulation Z section 1026.20, so a reset should never arrive unannounced. The calculator’s max-payment figure uses your lifetime cap: if that payment breaks the budget, the ARM is not for you, whatever the break-even says. The index behind most new ARMs is published by the Federal Reserve Bank of New York’s SOFR page, and the margin added to it is fixed at origination, which makes the margin the number worth haggling over when two ARM offers differ.

The break-even this tool reports, and the one it does not

The break-even here is a payments break-even: the month the ARM’s cumulative monthly payments pass the fixed loan’s. It is not a total-cost break-even, and the difference matters near the crossover.

Because the ARM’s early payments carry less interest, its balance falls slightly faster than the fixed loan’s in the early years, and after a reset to a higher rate the position reverses. A comparison that also counted the remaining balance at your exit date, the approach fuller ARM analysers take, would put the true economic crossover a little later than year 13.2 on the example, since the ARM borrower who sells at year 10 leaves with marginally more equity than the payments alone suggest. This tool does not compute balances at the exit date, does not apply the periodic caps step by step, assumes one adjustment rather than annual repricing, and ignores taxes, insurance, closing costs and refinancing fees on both sides. None of that makes the payments break-even useless: it is the conservative version of the answer, the year the ARM stops winning on cash out of your account, and for a hold comfortably inside it the conclusion is safe. If your hold lands within a year or so of the break-even, treat the decision as genuinely open and price the exit properly, including what refinancing the ARM into a fixed loan would cost, with the cost to refinance mortgage calculator. If the ARM itself is the loan you already hold and you want its payment path on its own, the 10-year adjustable-rate mortgage calculator covers the single-loan side of the family.

When each loan wins

The ARM wins when your exit is scheduled before the break-even and the fixed loan wins when it is not. Everything else is a footnote to that sentence.

Notice what is missing from both lists: a prediction about where rates go next. A scenario rate is a test, not a forecast, so run three: the rate staying put, the rate at the cap, and one in between. If the ARM only wins in the kind scenario, the fixed loan’s premium is buying insurance. The Federal Reserve’s Consumer Handbook on Adjustable-Rate Mortgages makes the same point: choose the ARM only when the worst case fits the budget.

What this calculator covers, and why each part matters

This calculator answers one question on one screen: for your scenario, in which year do the ARM’s early savings run out, and what is the worst case if rates reach your cap?

• A payments break-even, stated as a year. The comparison adds up the monthly payments on both loans and reports the first month the ARM’s cumulative payments pass the fixed loan’s. It is measured on payments, not on interest alone, because the fixed loan’s higher early payments are partly principal.
• Your scenario rate, not a preset path. You enter the rate you want to test at the first reset — today’s fully indexed rate for a neutral case, a higher number for a stress test — and the model adjusts once to that rate and holds it.
• The banked savings in dollars, beside the worst-case payment. The early monthly savings are totalled for you, and the payment at your lifetime cap sits next to the break-even year, so the budget test and the crossover year are visible together.
• Limits declared on the page. Both loans are 30-year loans, the model makes one adjustment, and it does not adjust for the remaining balance at exit. Those choices are stated on the page, so you know exactly what the break-even year does and does not include.

To see a single loan’s month-by-month schedule behind either side of the comparison, the amortization schedule calculator shows every payment’s split.

Three questions before you sign an ARM

Answer these three in order and the ARM decision usually makes itself.

Frequently asked questions

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References