As long as you file on time, and pay as much as you can when you file, the interest and penalties on the unpaid balance is a penalty of 0.5% per month, plus interest currently at 7.7% APR (roughly 0.6% per month). If you don't file on time, the penalty jumps to 5% per month.
If you can pay in full in less than 6 months, you can request a short term payment plan for free, but the only benefit is you don't get a bill, the interest and penalties still accrue at the normal rate.
If it will take longer than 6 months to pay, there is a non-refundable application fee for a long-term payment plan, and the interest and penalties are reduced by about half.
