How to pay the federal interest penalty.

[komocode]

I filed for an extension on federal and state. I'm now filing my taxes and paying the balance owed (which is fairly large) on federal state. 

Question is how do I pay the interest? Will IRS and California send me a bill after I file or do I need to calculate manually the interest on the balance and send along with my tax filing?

[DoninGA · Accepted solution]

The IRS and the State will send you a bill in the mail for any penalties and interest owed after they receive the tax returns and your payment.

[Horontax2018]

Can I pay by bank account check routing number if I file by the extension date (Oct 15) and E-file to pay income tax with interest (penalties)?

[Mike9241]

you can use Direct Pay and the reason is balance due.   most likely you will not compute the penalty correctly which means you'll either get a refund or a bill.