I never paid our $1089 we owed for Federal last year, can I add that to this year's amount I pay?

[xmasbaby0]

Did you file your 2015 tax return, but not pay the tax due?

[jamieschreck123]

I filed, but didn't pay

[xmasbaby0]

You are going to owe interest/penalty besides the original tax due amount.
In case you need  a payment plan: <a rel="nofollow" target="_blank" href="https://www.irs.gov/individuals/payment-plans-installment-agreements">https://www.irs.gov/individual...>

[BobB7 · Accepted solution]

Do not just add it to what you pay with the 2016 return. They will get confused about what tax year to apply it to!

Instead, fill out a 1040-V for 2015 and mail in in in its own envelope. https://www.irs.gov/pub/irs-prior/f1040v--2015.pdf

Eventually, they will send you a bill for interest and, maybe, penalties.