Brianna timely filed her 2018 tax return on March 1, 2019. She had a balance due, which she paid on April 15, 2019. She later determined that she had failed to claim an education credit for which she was eligible. The credit would have reduced her tax liability that year. The latest Brianna can file an amended return to correct the originally filed 2018 return and claim the credit is: March 1, 2021. April 15, 2021. March 1, 2022. April 15, 2022.