Most funding opportunity announcements (FOAs) have a two-week late window of consideration during which time an application can be submitted. However, the terms are very specific, and don’t apply to some Requests for Applications (RFAs). Examples of reasons why late applications might be accepted include Review Service, Illness, Natural Disasters etc. However, no advance permissions can be given for late applications. You should list your reasons in the cover letter with your application and the decision will be made on a case-by-case basis. You should read the NIH late policy in the NIH Guide Notice NOT-OD-15-039 for an explanation of how the policy may apply to you.
In addition, some reviewers have continuous submission eligibility because they are appointed to an NIH review group such as a study section or institute advisory council or have “recent substantial service.” Under continuous submission, these reviewers may submit R01, R21, and R34 applications with standard due dates at any time during the council round. Read the NIH continuous submission policy in both NOT-OD-17-042 and NOT-OD-18-178 if this policy applies to you.