How to pay the federal interest penalty.

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?

Get your taxes done using TurboTax

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.

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Get your taxes done using TurboTax

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)?

Get your taxes done using TurboTax

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.