I under put HSA funds in for 2020 ($4375.00), Am I allowed to put additional funds ($2725.00) in this year 2021 to count towards my 2020 family limit?
assuming you're qualified to make the max for family coverage you have until 4/15/2021 to make a contribution for 2020. yes you must tell the trustee/custodian that the $2725 is for 2020.