If you mean you owe and need to make payments to the IRS then you should put down as much as you can afford so you pay off the debt as fast as possible ... the interest and penalties continue to accrue on the unpaid balance at a rate of about 22% per month ... like a really bad credit card. So if you don't pay in enough you will never pay it off.
Next piece of advice ... do NOT use the payment plan option in the TT program ... instead choose to pay the balance due by check then you have until 7/15 to make any kind of payment you can. Then if you do not pay in full the IRS will send you a bill for the balance due ... if you are going to pay it off in the next 6 months or so then simply make a payment and wait for the next bill to arrive and repeat the process until the taxes are paid in full. You are NOT required to get on a payment plan as long as you keep making payments of some kind regularly.
If you do want/need to get on a payment plan then do so directly on the IRS site as the fees to do are lower than going thru TT ... https://www.irs.gov/payments/online-payment-agreement-application
