If you are not able to pay the tax you owe by your original filing due date, the balance is subject to interest and a monthly late payment penalty. There is also a penalty for failure to file a tax return, so you should file timely even if you cannot pay your balance in full. It is always in your best interest to pay in full as soon as you can to minimize the additional charges. This article will discuss U.S. federal tax payment options for your reference.

You can choose to pay the tax electronically or by mail. Paying electronically is a convenient way to pay your federal taxes online, by phone for Electronic Federal Tax Payment System (EFTPS) or card payments, or from a mobile device. When paying electronically, you can schedule your payment in advance. You will receive instant confirmation after you submit your payment. With Direct Pay and EFTPS you can opt in to receive email notifications about your payments. If you decide to pay by mail, enclose a check or money order with a copy of your tax return or notice. Make it payable to the United States Treasury and provide your name, address, daytime phone number, taxpayer identification number, tax year, and form or notice number (for example, 2020 Form 1040) on the front of your payment.

If you cannot pay in full, you should pay as much as possible to reduce the accrual of interest on your account. Or you may qualify for additional time --up to 120 days-- to pay in full. There is no fee for this full payment; however, interest and any applicable penalties continue to accrue until your liability is paid in full. If you still cannot pay the balance within 120 days, you may qualify for a monthly payment plan (including an installment agreement). To request a payment plan, use the OPA application, complete Form 9465, Installment Agreement Request.

Please note that if you do not pay your tax liability in full or make an alternative payment arrangement, the IRS has the right to take collection action. So, it is important to pay the balance (make payment arrangement) and respond to an IRS notice on time.

Reference:
https://www.irs.gov/taxtopics/tc202