April 15. It is not a seprate tax. If you were to file an extension, you would still be expected to pay on time. If you can't manage to pay it all by the filing date, you can request a Installment Agreement.
The best thing you can do is
pay it before April 15 this year. If you can't you can fill out Form 9465
Installment Agreement Request. You will be liable for penalties and interest.
Understand your
agreement & avoid default
- Your
future refunds will be applied to your tax debt until it is paid in full;
- Pay at
least your minimum monthly payment when it's due;
- Include
your name, address, SSN, daytime phone number, tax year and return type on
your payment;
- File all
required tax returns on time & pay all taxes in-full and on time
(contact us to change your existing agreement if you cannot);
- Make all
scheduled payments even if we apply your refund to your account balance;
and
- Ensure your statement is sent to the correct address, contact us
if you move or complete and mail Form 8822, Change of Address (PDF).
For complete information, see https://www.irs.gov/individuals/payment-plans-installment-agreements.
TurboTax will give
you this option during the Filing section
