IRS Form 5564, titled “Notice of Deficiency – Waiver,” arrives attached to a statutory notice of deficiency (the 90-day letter). Signing it tells the IRS you accept the proposed additional tax, waives your right to petition the U.S. Tax Court, and lets the IRS immediately assess and collect the amount shown. Don’t sign if you disagree with the numbers. Do sign if you agree and want to close the matter.1Internal Revenue Service. Understanding Your CP3219A Notice
What Form 5564 Actually Is
The form is a written waiver. Federal tax law normally bars the IRS from assessing additional tax until the 90-day petition window closes or you waive that restriction in writing. Your signature on Form 5564 is that waiver, and the statute lets you waive the restriction on “the whole or any part of the deficiency.”2Office of the Law Revision Counsel. 26 USC 6213 – Restrictions Applicable to Deficiencies; Petition to Tax Court
Because it comes with the statutory notice, the 90-day clock to challenge the deficiency in Tax Court is already running by the time you open the envelope. You have 90 days from the mailing date of the notice (150 days if you’re outside the United States) to decide what to do.3Taxpayer Advocate Service. 90 Day Notice of Deficiency
What You Give Up by Signing
The main thing you lose is access to the U.S. Tax Court. Tax Court is the only federal court where you can dispute a tax bill before paying it. Every other court that hears tax cases requires full payment up front. If you can’t easily write a check for the disputed amount, Tax Court is usually the only realistic place to argue your case, and signing Form 5564 closes that door.
Once the IRS receives your signed waiver, it formally assesses the deficiency on its records and starts collecting. A bill goes out, and the full collection toolkit becomes available, including liens and levies on bank accounts or wages.3Taxpayer Advocate Service. 90 Day Notice of Deficiency
What Signing Does to Interest
Interest on an unpaid balance runs from the original due date of the return until you pay it off. Signing doesn’t stop that interest. It does, however, give you one narrow protection: once the waiver is filed, the IRS has 30 days to send a notice and demand for payment. If the IRS takes longer than 30 days, interest is suspended between day 30 and the day the bill actually arrives. The suspension covers both interest on the deficiency and interest that had been accumulating on earlier interest.4Office of the Law Revision Counsel. 26 USC 6601 – Interest on Underpayment, Nonpayment, or Extensions of Time for Payment, of Tax
The benefit is real but limited. If the IRS bills you within the 30 days, there’s no suspension at all. Once the bill arrives, interest resumes until you pay. If minimizing interest is your motivation for signing, pay promptly when the bill lands.
The 10-Year Collection Period Starts Earlier
Assessment also starts the IRS’s 10-year countdown to collect. After the Collection Statute Expiration Date, the debt expires and the IRS can no longer pursue it.5Internal Revenue Service. Time IRS Can Collect Tax Signing Form 5564 triggers assessment sooner than fighting the case would, which means the clock starts sooner and the debt expires sooner. A taxpayer who litigates for two or three years before assessment faces a collection window that ends two or three years later.6eCFR. 26 CFR 301.6502-1 – Collection After Assessment
If You Sign but Can’t Pay
Signing commits you to the amount but doesn’t force immediate payment. If you can’t pay in full, the failure-to-pay penalty kicks in: 0.5% of the unpaid tax for each month or partial month the balance is outstanding, up to a 25% maximum. With an approved installment agreement in place, that rate drops to 0.25% per month. If the IRS issues a notice of intent to levy and you still haven’t paid 10 days later, the rate climbs to 1% per month.7Internal Revenue Service. Topic No. 653, IRS Notices and Bills, Penalties and Interest Charges
Payments are applied in a fixed order: tax first, then penalties, then interest. Partial payments shrink the underlying tax before touching anything that has accumulated on top of it.
Can You Still Fight It After Signing?
Yes, but only the hard way. Once you sign, Tax Court is off the table, so your remaining path is to pay the deficiency in full and then sue for a refund. The administrative step comes first: file an amended return (Form 1040-X for income tax) or, for penalties and interest, Form 843.8Internal Revenue Service. About Form 843, Claim for Refund and Request for Abatement If the IRS denies the claim or doesn’t act on it within six months, you can sue in U.S. District Court or the U.S. Court of Federal Claims.9Office of the Law Revision Counsel. 28 USC 1346 – United States as Defendant You can’t skip the administrative claim; without it, no court will hear the case.10Office of the Law Revision Counsel. 26 USC 7422 – Civil Actions for Refund
Refund claims have a strict deadline: three years from the date you filed the original return or two years from the date you paid the tax, whichever is later. If you never filed a return, it’s two years from payment.11Office of the Law Revision Counsel. 26 USC 6511 – Limitations on Credit or Refund For someone who signs and then pays years after the original return was due, the two-year-from-payment rule is typically what controls.
What Happens If You Don’t Sign
Not signing preserves your options, but it doesn’t buy you more time. The 90-day Tax Court deadline runs from the mailing date of the notice whether you sign or not. If day 90 passes without a filed petition, the IRS can assess and collect as if you had signed, and you’ll have lost the interest-suspension benefit along the way.
The deadline is absolute. Neither the IRS nor the Tax Court can extend it. Doing nothing is the worst outcome: no judicial review, no interest benefit. If you disagree with the deficiency, file the petition. If you agree, sign the waiver. Letting the clock run out gains you nothing.
While a Tax Court petition is pending, the IRS cannot assess or collect the deficiency. That built-in freeze is a large part of why Tax Court matters to taxpayers who want to contest without paying first.
Joint Returns
When the deficiency comes from a joint return, both spouses generally need to sign for the waiver to bind both. If only one signs, the IRS can still assess against the signing spouse, but the non-signing spouse keeps the right to petition Tax Court for their share. Spouses can take different positions on the same notice.
If you agree with the deficiency but have additional income, deductions, or credits the IRS didn’t account for, you can submit Form 1040-X together with Form 5564. Write “CP3219A” at the top of the amended return so the IRS processes both documents together.1Internal Revenue Service. Understanding Your CP3219A Notice
So Should You Sign?
Sign if you agree with the IRS’s numbers and want the matter closed. Signing ends the procedural back-and-forth, activates the interest-suspension protection if the IRS is slow to bill, and starts the 10-year collection clock so the debt has an end date. If the notice shows the IRS owes you money, signing speeds the refund.
Don’t sign if you dispute any part of the deficiency. Your only remaining path after signing is pay-first-then-sue, which is slower and more expensive than Tax Court. The common mistake is treating Form 5564 as routine paperwork. It is a legal waiver with lasting consequences, and the 90-day window gives you time (but not unlimited time) to get advice before you commit.