I could be horribly wrong about MD tax due date, but I believe it was due yesterday. You must file extension on or before the due date for the tax return. 

I would have the client log onto https://interactive.marylandtaxes.gov/individuals/payment/ and make an estimate tax payment for 2021 to cover the tax due. Alternatively give them a 2021 estimate tax voucher and have them mail it. 

George - you are horribly wrong.  Well, at least the due date part.  Maryland got a reprieve from their governor and the due date has been kicked down the road aways.

Well that is not my only horrible misteak! 

Does this also mean the federal due date is extended? 

Be sure to complete the bank information in screen 3. and check the box for Maryland Direct ... for Electronic payment of tax due with extension. 

In screen 9 do NOT enter 1= automatic extension (for federal, because I think this will cause reject. For Maryland information check the box for e-file MD extension. and you can complete the information for the amounts as Overrides to make sure you have what you want the extension to show. This way it will not change when you finalize the return. 

When all is good, use E-File > Start Extension Wizard

No. MD individuals have until July 15. Federal was due April 18.