ARM vs Fixed 5 Year Cost Calculator

An ARM may offer a lower starting rate, which can create lower payments during the early years. A fixed rate mortgage may start higher but provides predictable principal and interest payments throughout the five year period.

The ARM vs Fixed 5 Year Cost Calculator from Merchants Home Lending helps compare these two loan structures over a specific five year window. Instead of looking only at the initial monthly payment, it examines the money paid, interest accumulated, principal remaining, and potential ARM adjustments during the first five years.

Why Five Years Is a Useful Comparison Period

Five years is long enough to reveal more than the initial ARM payment while still representing a common short to medium term planning horizon.

For example, a homeowner may expect to:

• Sell within five years
• Relocate for work
• Refinance before a later adjustment
• Keep the property as a rental
• Reassess the mortgage after several years
• Compare an ARM with a fixed loan before purchasing

The five year window can show whether the ARM's initial savings remain meaningful after considering the loan balance and other costs.

Compare the Two Loans Side by Side

The calculator starts with the actual terms of both mortgages.

ARM

Enter:

• Loan amount
• Initial interest rate
• Initial fixed period
• Adjustment frequency
• Index
• Margin
• Periodic rate cap
• Lifetime rate cap
• Points
• Closing costs

Fixed Rate Mortgage

Enter:

• Loan amount
• Fixed interest rate
• Loan term
• Points
• Closing costs

The comparison should use equivalent loan amounts and comparable cost assumptions whenever possible.

The Four Numbers That Matter After Five Years

A useful five year comparison should produce more than two monthly payments.

Look at:

Total principal and interest paid

How much money was paid toward the mortgage during the five year period.

Total interest paid

How much of those payments represented interest.

Principal remaining

How much would still be owed after five years.

Net five year cost

The combined effect of payments, upfront costs, and remaining loan balance under the selected assumptions.

This gives a much clearer picture of the two mortgage structures.

Example of the Five Year Comparison

Consider an illustrative $400,000 mortgage.

‍

The actual results depend on the loan terms and the ARM's future rate assumptions.

The purpose of the comparison is to determine whether the ARM's initial advantage remains meaningful after five years.

Don't Judge the ARM by the First Payment

Suppose the ARM starts $250 below the fixed mortgage payment.

It is tempting to multiply that difference by 60 months and call the result the five year savings.

That can be misleading.

The ARM may adjust before the five year period ends.

The outstanding balance can also differ between the two loans.

Closing costs and points can further change the comparison.

A proper five year calculation therefore needs to follow the mortgage month by month rather than simply multiplying the initial payment difference by 60.

What Happens If the ARM Has Not Adjusted Yet?

Some ARM structures remain at their introductory rate for five years or longer.

If the initial fixed period extends through the full five year window, the comparison becomes relatively straightforward.

You can focus on:

• Initial rate
• Monthly payment
• Total interest
• Principal reduction
• Upfront costs
• Remaining balance after 60 months

In that scenario, the five year calculation is primarily about comparing the economics of the two loan structures before the ARM begins adjusting.

What If the ARM Adjusts During the Five Years?

This is where the comparison becomes more sensitive.

Suppose the ARM begins adjusting after three years.

The first 36 months may benefit from the lower introductory rate.

Months 37 through 60 then depend on the ARM's adjustment formula and the assumed future index.

You should therefore model the final two years using a specific rate scenario rather than assuming the initial rate continues unchanged.

Test More Than One ARM Scenario

Future interest rates are unknown.

Instead of entering one future rate and treating it as certain, compare several possibilities.

Stable Rate Scenario

The ARM remains relatively close to its starting rate.

Moderate Increase

The ARM adjusts higher after the initial period.

Higher Rate Scenario

The ARM experiences a more substantial increase within its contractual limits.

This gives you a range of five year outcomes.

The scenarios are not predictions. They show how sensitive the five year comparison is to future ARM rates.

The Remaining Balance Changes the Calculation

Imagine the ARM has produced $15,000 less in payments after five years.

That does not automatically mean the borrower is $15,000 better off.

Suppose the ARM also has a $10,000 higher remaining principal balance.

The true financial comparison is more complicated than the payment difference alone.

This is why the calculator should show the remaining mortgage balance at the five year mark.

A mortgage with lower payments can still leave a different amount owed at the end of the comparison period.

Closing Costs Belong in the Calculation

Upfront expenses can materially change the five year result.

For example:

ARM

• Lower interest rate
• $5,000 in points and costs

Fixed

• Higher interest rate
• $2,000 in points and costs

The ARM's lower monthly payment must first overcome its additional upfront expense before the difference becomes a net savings.

The calculator should therefore include:

• Discount points
• Lender charges
• Other applicable refinance or purchase costs
• Credits

Use actual estimates whenever they are available.

Five Year Cost Is Not the Same as Lifetime Cost

This calculator intentionally focuses on the first five years.

That means an ARM can appear less expensive during this period even if it becomes more expensive later.

For example:

Years 1 to 5

ARM has lower modeled cost.

Years 6 onward

Future ARM adjustments create additional payment exposure.

That does not make the five year calculation wrong. It simply answers a different question.

If you expect to keep the mortgage beyond five years, extend the analysis to match your expected holding period.

What If You Sell After Five Years?

A five year sale can make the remaining mortgage balance particularly important.

Suppose:

• Home value at sale: $600,000
• Fixed loan balance: $350,000
• ARM balance: $345,000

Before selling expenses and other transaction costs, the ARM would leave a slightly smaller mortgage balance.

But if the ARM also required higher payments or greater upfront costs under the selected scenario, the overall comparison could look different.

This is why the calculator should consider the complete five year cost, not one isolated number.

What If You Refinance Before Five Years?

The same principle applies.

If you expect to refinance after three years, a five year comparison may not represent your actual mortgage strategy.

Use the calculator to see the five year picture, but also test your expected refinance date.

For example:

• Three year cost
• Five year cost
• Seven year cost

This can show whether the ARM's advantage depends on keeping the loan for a specific period.

Payment Stability Is Part of the Comparison

Not every mortgage decision is purely about the lowest projected cost.

A fixed rate mortgage provides a predictable principal and interest payment.

An ARM introduces the possibility of future payment changes.

That difference should be visible alongside the financial calculations.

For example:

‍

The table describes the structural difference rather than predicting which option will cost less.

A Five Year Stress Test

A useful way to use the calculator is to run three versions of the ARM.

Base case

Use your central rate assumption.

Higher rate case

Assume the ARM adjusts upward after its introductory period.

Severe case

Model a larger increase within the loan's contractual limits.

Then compare all three with the fixed mortgage.

If the ARM remains competitive across several reasonable assumptions, you have a broader understanding of its potential five year economics.

If the result changes dramatically with a small rate adjustment, that sensitivity is equally important.

Don't Assume Refinancing Will Solve the ARM Risk

A borrower may think:

“I will take the lower ARM rate now and refinance before it becomes expensive.”

That may happen, but it should not be treated as guaranteed.

Future refinance rates, home value, income, credit, closing costs, and qualification requirements can all affect the outcome.

A stronger five year analysis includes at least one scenario where the borrower keeps the ARM according to its contractual terms.

Who May Find This Calculator Useful?

The calculator can be useful if you are:

• Comparing an ARM and fixed mortgage before buying
• Planning to own a property for around five years
• Considering an ARM with a five year initial period
• Evaluating whether initial ARM savings justify future uncertainty
• Comparing loan offers with different upfront costs
• Planning a potential sale or refinance
• Testing different future ARM rates

It is particularly useful when the expected holding period is known but the future interest-rate environment is not.

Frequently Asked Questions

What does an ARM vs fixed five year cost calculator measure?

It compares the projected financial cost of an ARM and fixed rate mortgage over the first five years, including payments, interest, remaining balance, and applicable upfront costs.

Why compare mortgages over five years?

Five years can provide a useful short to medium term window for borrowers who expect to sell, refinance, or reassess their mortgage within that period.

Does a lower ARM payment mean it will cost less after five years?

Not necessarily. The ARM's future adjustments, upfront costs, interest paid, and remaining balance can all affect the five year result.

What if my ARM does not adjust during the first five years?

Then the comparison can focus primarily on the initial rate, payments, costs, interest, and principal balance during the five year period.

What if my ARM adjusts before five years?

The calculator should include an assumed future rate path based on the ARM's index, margin, caps, and adjustment schedule.

Should I include closing costs?

Yes. Including points and applicable transaction costs gives you a more realistic five year comparison.

Does this calculator predict future ARM rates?

No. Future rates are uncertain. The calculator uses assumptions to model different possible outcomes.

Is the five year result enough to choose between an ARM and fixed mortgage?

It depends on your expected plans. If you expect to keep the mortgage longer than five years, you should also examine longer holding periods and higher rate scenarios.

See the Five Year Cost Before Choosing the Loan

The initial ARM rate can make a noticeable difference during the first few years, but the real comparison requires more than looking at the starting payment.

The ARM vs Fixed 5 Year Cost Calculator from Merchants Home Lending lets you examine the first 60 months from several angles: payments made, interest paid, principal remaining, upfront costs, and potential ARM adjustments.

Run a stable rate scenario and at least one higher rate scenario. Then compare the results with the fixed mortgage over the same five year period.

The five year cost gives you a clearer picture of what you are paying today, what you may still owe later, and how much future ARM rate movement could matter.