ARM worst-case calculator

See the highest payments an adjustable-rate mortgage allows. Enter the terms from your Loan Estimate’s Adjustable Interest Rate (AIR) table. Every box starts blank, including the rate: this site doesn’t supply rates.

Calculate the highest rate and payment under the caps

The loan

Loan amount Dollar amount.

Loan term (years) Whole number of years, for example from your note. Up to 50.

Starting interest rate (%) The initial interest rate a lender quoted you. This site does not supply rates.

When the rate can change

Fixed-rate period How long the starting rate lasts. Whole number.

Fixed-rate period entered inThe AIR table shows the first change as a month number, such as the 61st month (a 60-month fixed period).

How often the rate can change after that“Subsequent changes” on the AIR table.

Rate caps (percentage points)

Caps are sometimes written as three numbers, first / subsequent / lifetime, for example 2/1/5. Enter each number in its own box. 0 is allowed.Source: CFPB: “Adjustable-Rate Mortgages” booklet (Consumer Handbook on Adjustable-Rate Mortgages, last updated September 2026) · checked Nov 10, 2026

First adjustment cap Most the rate can rise at the first change.

Subsequent adjustment cap Most the rate can rise at each later change.

Lifetime cap Most the rate can ever be above the starting rate.

What this calculator does and doesn’t do

Assumes the rate rises by the most the caps allow at every scheduled change, up to the starting rate plus the lifetime cap. Real changes follow the index plus the margin and can be smaller, or go down.Source: CFPB: “What are rate caps with an adjustable-rate mortgage (ARM), and how do they work?” (Ask CFPB #1951, last reviewed Jan 14, 2025) · checked Nov 10, 2026
Refigures principal and interest at each change so the remaining balance is paid off over the remaining months (a fully amortizing loan). It doesn’t model payment caps, interest-only periods, negative amortization, or a rate floor.
Also shows the payment if the whole loan amount were repaid at the maximum rate over the full term, as a simple ceiling for comparison.
Principal and interest only: taxes, insurance, mortgage insurance, and HOA dues aren’t included. Amounts are rounded to the cent for display.
Runs entirely in your browser. Nothing you type is sent anywhere or saved.

Compare the results with the AIR and Projected Payments tables on your Loan Estimate.Source: 12 CFR 1026.37(c) and (j), and 1026.38(c) and (n) (Regulation Z: Projected Payments and Adjustable Interest Rate tables) · checked Nov 10, 2026 For how caps work and the program rules, see ARMs: the worst case under the caps.

Guidelines change; confirm with a licensed lender.