Mortgage calculator

ARM worst-case payment calculator

An ARM’s caps set the most the rate can rise. This shows the payment if it rises that far, as fast as allowed.

Your numbers

Enter your loan’s own start rate and caps (a 30-year loan). Nothing you type leaves this page.

Rates filled in from Freddie Mac’s Primary Mortgage Market Survey® 30-year average of 7.40% for the week of October 8, 2026: national averages, not a quote. Enter the rate you were quoted. This product uses the FRED® API but is not endorsed or certified by the Federal Reserve Bank of St. Louis.

Adjusts every
–Enter the loan, start rate, fixed period and caps to see the worst case.

An estimate only, not a loan offer. Your Loan Estimate from the lender is the figure to rely on.

How it works

Worst-case rate = start rate + the most each cap allows, until the lifetime cap

After the fixed period the rate rises by the first cap, then by the later cap at each adjustment, never above start rate plus lifetime cap. The payment is recalculated on the remaining balance each time. Enter a fixed rate to compare: the saving during the fixed period against the worst case afterwards.

Keep in mind

  • This is the ceiling, not a forecast: the actual rate follows the index plus the margin, and can also fall.
  • Interest-only ARMs work differently and are not covered here.

Questions

What do ARM caps like 2/1/5 mean?

The rate can rise at most 2 points at the first adjustment, 1 point at each later one, and 5 points in total over the life of the loan.

Is a 5-year ARM risky?

The risk is the payment after the fixed period. If you will sell or refinance before then, or can afford the worst case shown here, the lower start rate can be worth it.

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Want a real number?

This ARM worst-case payment calculator gives you a good estimate. Jack can run your actual scenario against current lender guidelines and show you the options, free.

Jack Gladden
Jack GladdenSenior Loan Officer · NMLS #1470164
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