“Is a funding opportunity announcement’s expiration date also the deadline to apply?”

No, the expiration date listed in a funding opportunity announcement (FOA) or notice of special interest (NOSI) and indexed at Opportunities & Announcements is when the FOA or NOSI will switch from “active” to “inactive” in NIH’s electronic systems. Generally, the expiration date is one day after the FOA’s or NOSI’s final due date, meaning an application submitted on the expiration date is late and NIH may not accept it.