You will receive a letter from the IRS once your payment plan has been accepted, and your automatic debits will begin after that. Please note that this can take up to three months to process, and penalties and interest on the unpaid balance will accrue during this time.
While you are not required to do so, you are able to begin
sending payments before you receive the letter (in addition to your initial
payment). If you do so, make sure that
your check has your social security number and the tax year to which the
payments should be applied. It would
also be a good idea to include a short note indicating that you are making a
payment toward your 2018 (or applicable year's) balance.
Note: You should pay
as much of the outstanding balance as you are able to (even if it is not the
full amount) before April 15, 2018, to reduce the amount of interest and
penalties that will be applied to your account.
You will be assessed an underpayment penalty for any amount of unpaid
tax, which will be assessed based on the balance due as of April 15. Additionally, the IRS will begin to assess
interest on the unpaid balance then.
[Edited 4/10/19 | 10:05am]