How long do I have to respond to IRS CP518B?

Respond promptly using the enclosed envelope. Check the date and any response deadline printed on your notice, and follow the notice's instructions.

What should I do if I received IRS CP518B?

Mail a signed paper return with all schedules and the enclosed Response form, or use the form to explain why no return is due. If you are unsure, have a tax professional review the letter before you respond to the IRS.

IRS CP518B Notice: Final Reminder for an Unfiled Business Return

Final reminder that the IRS has no record of your business's prior return. File a signed paper return with the response form or the IRS may figure the tax for you.

Published by the Law Offices of Darrin T. Mish, P.A.Updated October 13, 2026

Notice: CP518B
Urgency: Urgent
Deadline: Respond promptly using the enclosed envelope

Your first move

Mail a signed paper return with all schedules and the enclosed Response form, or use the form to explain why no return is due.

What This Notice Means

This is a final reminder. The IRS still has no record that your business filed its prior tax returns.

What to Do

Send a signed paper tax return with all required schedules.
Complete and return the Response form that came with your notice.

Use the Response form to explain one of these:

Why you're filing late.
Why you believe you don't need to file.
That you already filed and more than four weeks have passed.
That you filed under a different name or employer ID number (EIN) than the one on the notice.

Send everything in the enclosed envelope, or fax it to the number provided on your notice. If you use an online fax service, understand its privacy and security policies first.

If you filed within the last four weeks using the same name and EIN shown on the notice, you can disregard it. Make sure the name, identifying number, and tax year on your return match the notice.

If You Don't Respond

The IRS may determine your tax for you. Penalties and interest can continue to build. Any refund owed to you for the current year or a prior year may be held up because of the unfiled return.

A tax figured by the IRS won't include the deductions and credits you'd claim yourself. That's the main reason to file your own return now.

If You Owe and Can't Pay

File anyway. You can request a payment plan. You can also look at whether an offer in compromise fits.

If You Disagree

Call the number on your notice. Have your paperwork ready.

Before You Respond

Confirm which returns the business actually filed.
Check whether a return went in under a different EIN or business name.
Keep a copy of everything you send and proof of mailing.

If your business has unfiled returns and the IRS is pressing, call us at (813) 229-7100.

This letter has a clock on it. Don’t run it out alone.

Free consultation with Darrin T. Mish, a Tampa tax attorney licensed since 1993 and admitted to the U.S. Tax Court. Bring the letter.

Call (813) 229-7100

Request a consultation online