Use the expiration date printed on the actual visa; State Department guidance requires entry before it expires.
Read the document rather than use a generic validity estimate
Keep the real visa and official instructions accessible. A date copied into an old relocation spreadsheet should be checked against the issued document before it drives tickets, housing or employment commitments. Distinguish the window during which a visa remains valid for travel from the separate period of admission granted on arrival, since the two run on different rules and a visa can remain unused within its own validity even as other circumstances change.
Note that an admission record issued at the border can authorize a shorter or longer stay than the visa's own validity window suggests, so the two dates should never be treated as interchangeable. A family travelling together should not assume every member's document carries the same dates: check each visa individually, because one person's document can expire before another's even when both were issued around the same time. Keep the physical document itself, not a photograph or a note copied from it, as the source consulted before finalizing any booking, and recheck it again close to the travel date rather than relying on an earlier check.
Where a date on the document looks unclear or inconsistent with other paperwork, raise it through the official process before travel rather than guessing which one controls.