For a borrower with an interest rate cap structure on an adjustable‑rate mortgage (ARM), the maximum change at the very first reset is set by the initial adjustment cap in the cap structure (e.g., the “2” in a 2/1/5 structure means a maximum 2‑percentage‑point move at the first adjustment).

What “cap structure” means

  • ARMs typically show caps in a three‑number format such as 2/1/5 or 5/2/5, which correspond to initial adjustment cap / periodic (subsequent) cap / lifetime cap.
  • This structure limits how much the interest rate can move at the first adjustment, at each later adjustment, and over the life of the loan as a whole.

Maximum adjustment on the initial reset

  • The maximum initial adjustment is exactly the first number in that cap structure, expressed in percentage points above or below the original start rate (for example, 2% in a 2/1/5 cap, 5% in a 5/2/5 cap, etc.).
  • In practice, common initial caps are in the 2%–5% range, so a loan starting at 4% with a 2% initial cap could adjust at the first reset to no higher than 6% and no lower than 2%, even if the index movement would otherwise justify a bigger change.

Small numeric example

  • Suppose the note says the cap structure is 2/1/5 and the initial fixed rate is 3.5%.
  • At the first adjustment date, the new rate is constrained so it cannot be more than 2 percentage points above or below 3.5%, meaning a maximum of 5.5% on the upside (or 1.5% on the downside, if the index fell a lot).

Quick table of common caps

[7][1][3] [5][1][3][7] [1][5][7] [9][3][7] [3][7][9] [7][9][3] [9] [9] [9]
Cap structure Max initial adjustment Typical use
2/1/5 ±2 percentage points at first reset Common on many conforming ARMs
5/2/5 ±5 percentage points at first reset Used on some higher‑risk or non‑standard ARMs
2/5/9 ±2 percentage points at first reset Illustrative structure in ARM education examples

TL;DR

  • Look at the first number in the cap structure (e.g., the “2” in 2/1/5 or the “5” in 5/2/5).
  • That number is the maximum allowed adjustment (in percentage points) to the interest rate at the initial adjustment.