When is the IRS mailing deadline for the ACA forms (1095-B and 1095-C)? Deadline to mail the ACA forms (1095-B and 1095-C) to recipients is March 4th, 2019 for the 2018 tax season. Note: If a deadline falls on a weekend day it is extended to the next business day. Have more questions? Submit a request 0 Comments Article is closed for comments.