20 CFR 404.322 : Employees' Benefits (§ 1.1 To Parts 1011-1099) — (Part 400 To Part 499) — Social Security Administration (Part 400 To Part 499) — Federal Old-Age, Survivors And Disability Insurance (1950- ) (§ 404.1 To § 404.2127) — Old-Age, Disability, Dependents' And Survivors' Insurance Benefits; Period Of Disability (§ 404.301 To § 404.392) — Old-Age And Disability Benefits (§ 404.310 To § 404.325) — When you may apply for a period of disability after a delay due to a physical or mental condition.

If because of a physical or mental condition you did not apply for a period of disability within 12 months after your period of disability ended, you may apply not more than 36 months after the month in which your disability ended. Your failure to apply within the 12-month time period will be considered due to a physical or mental condition if during this time -

(a) Your physical condition limited your activities to such an extent that you could not complete and sign an application; or

(b) You were mentally incompetent.