It's way too late to get an extension for 2020, but you don't need an extension for a refund. However, to get a refund for 2020 you must file your 2020 tax return by May 17. You cannot get a refund for 2020 after that date. See the following IRS news release for more information.
Time running out to claim $1 billion in refunds for tax year 2020, taxpayers face May 17 deadline
