The DTI ceilings are the same as any other loan. What changes on an ARM is the payment you have to qualify on, and for shorter ARMs that payment is higher than the first-year payment. On conventional loans, Fannie Mae's rule works like this: - Initial fixed period of five years or less (a 3/6 or 5/6, for example): you qualify at the greater of the note rate plus the first rate-adjustment cap, or the fully indexed rate, meaning the index plus the margin. - Initial fixed period longer than five years (a 7/6 or 10/6): you generally qualify at the note rate itself, with an exception for higher-priced loans, which use the greater of the note rate or the fully indexed rate. FHA and VA set their own qualifying-rate rules for ARMs, so ask how your specific program handles it rather than assuming the conventional math applies. Why this matters: an ARM is a tool for keeping your payment lower in the early years of ownership. Underwriting already assumes the payment can rise, so an ARM will not qualify you for a bigger loan, and a plan that depends on the low intro payment to squeeze into the house will not survive the qualifying math. If you are weighing an ARM against a fixed loan, we can show you both side by side in the free Roadmap conversation, where we run your real numbers.