I e-filed an extension, can I e-file my Federal return at the same time?

[allenlion]

I simply filed for an extension because my tax due was much greater than we expected. Our employer screwed up my withholding, after I revised it to reduce how much I pay every year. Their negligence resulted in my withholding being insufficient, increasing how much more I had to pay for 2018 Therefore we don't have the money to pay it right now & have to get with a financial adviser to see if I have to borrow against my TSP retirement fund. We're pretty angry with our employer right now.

[TomK]

Unfortunately, I may have more bad news (but I would rather you know it now then be surprised later).  

Filing an extension does NOT give you more time to pay your tax balance due.  If you do not pay by April 15, 2019, any balance still due will be subject to interest (it will keep you from getting a late filing penalty).

You can file for an installment plan to make payments for any balance due (but again, any balance not paid by 4/15 is still subject to interest).

What if I can't pay my taxes?: https://ttlc.intuit.com/replies/3301261