IRS Letter 525 is a Statutory Notice of Deficiency, the formal letter the IRS must send before it can legally assess and collect additional tax it believes you owe. It gives you 90 days from the mailing date to file a petition in U.S. Tax Court and challenge the proposed amount without paying first. That 90-day window is the single most important thing in the letter, and letting it expire forfeits your right to a prepayment court challenge.
What Letter 525 Actually Is
The IRS issues Letter 525 after an audit where you disagreed with the results, or after you failed to respond to earlier adjustment proposals. By the time the letter arrives, the IRS considers its administrative process finished. The notice is your legal ticket into U.S. Tax Court, where you can dispute the tax without paying it up front.1Office of the Law Revision Counsel. 26 U.S. Code 6213 – Restrictions Applicable to Deficiencies; Petition to Tax Court
Under federal law, the IRS cannot assess or begin collecting the proposed tax until it has mailed this notice and the response period has run out. If you file a Tax Court petition in time, the IRS is blocked from collecting until the court issues a final decision.1Office of the Law Revision Counsel. 26 U.S. Code 6213 – Restrictions Applicable to Deficiencies; Petition to Tax Court That protection exists because it would be unfair for the IRS to seize your money while a court is still deciding whether you owe it.
What’s Inside the Notice
The notice includes a calculation of the additional tax the IRS says you owe, plus any penalties and interest. Attached to it is a detailed explanation of the specific changes the IRS made to your return, usually on Form 886-A (Explanation of Items) or Form 4549 (Income Tax Examination Changes). These attachments spell out which deductions were disallowed, which income was added, or which credits were adjusted.
Read the explanation line by line. The IRS sometimes groups multiple adjustments into one notice, and you may agree with some changes but not others. You’re allowed to contest only the items you disagree with and accept the rest.
Interest and Penalties
Interest on unpaid tax runs from the original due date of the return, not from when you receive the notice, and it compounds daily.2Office of the Law Revision Counsel. 26 USC 6622 – Interest Compounded Daily The IRS sets the underpayment rate each quarter based on the federal short-term rate plus three percentage points; for the first quarter of 2026 the rate is 7 percent, dropping to 6 percent in the second quarter.3Internal Revenue Service. Quarterly Interest Rates Interest keeps accruing even while a Tax Court case is pending.
The most common penalty attached to a deficiency notice is the accuracy-related penalty, which adds 20 percent of the underpayment attributable to negligence, a substantial understatement of income, or certain other errors.4Office of the Law Revision Counsel. 26 U.S. Code 6662 – Imposition of Accuracy-Related Penalty If the IRS believes the understatement was intentional, a civil fraud penalty of 75 percent can apply instead.
The 90-Day Deadline
You have exactly 90 calendar days from the date the IRS mailed the notice to file a petition with the U.S. Tax Court. If the notice was addressed to you outside the United States, the window extends to 150 days.5Office of the Law Revision Counsel. 26 USC 6213 – Restrictions Applicable to Deficiencies; Petition to Tax Court The countdown starts from the mailing date printed on the notice, not the date you receive it. If the last day falls on a Saturday, Sunday, or legal holiday in the District of Columbia, the deadline moves to the next business day.
This deadline has historically been treated as jurisdictional, meaning the Tax Court simply cannot hear your case if the petition arrives late. Courts have refused to grant extensions even in sympathetic circumstances. One protective detail: if the IRS prints a deadline date on the notice that happens to be later than the statutory 90-day calculation, filing by the date shown on the notice counts as timely.5Office of the Law Revision Counsel. 26 USC 6213 – Restrictions Applicable to Deficiencies; Petition to Tax Court Always check the date on the notice itself and use whichever deadline is later.
Verify Your Address on File
A valid notice of deficiency must be mailed to your “last known address.” Under the statute, mailing to that address is legally sufficient even if you never actually receive the letter.6Office of the Law Revision Counsel. 26 U.S. Code 6212 – Notice of Deficiency Your last known address is typically the address on your most recent tax return. If you’ve moved and haven’t filed a return with the new address or submitted Form 8822 (Change of Address), the IRS may send the notice to your old address, and the 90-day clock still starts ticking. Check your IRS account online or call the IRS to verify what address they have on file.
Proving You Filed on Time
If you mail your Tax Court petition, the postmark date counts as your filing date, but only if you use the U.S. Postal Service or an IRS-approved private delivery service. Approved services include specific FedEx, UPS, and DHL Express options listed on the IRS website.7Internal Revenue Service. Private Delivery Services (PDS) Standard ground shipping does not qualify. A privately metered postmark also does not count; you need an official USPS postmark or a tracking record from an approved service. Use certified or registered mail and keep the receipt. If your filing comes down to the wire, electronic filing through the Tax Court’s DAWSON system is often the safest route, since it timestamps your submission automatically.
Filing a Tax Court Petition
Filing a petition is less complicated than most people assume. The Tax Court offers three ways to do it: answer guided questions online through DAWSON and let it generate your petition, download and complete the court’s simplified petition form (Form 2), or draft your own petition following the court’s rules.8United States Tax Court. Guidance for Petitioners: Starting a Case
Whichever method you choose, explain clearly why you disagree with the IRS’s proposed changes. List each disputed item separately with a brief statement of the facts supporting your position. You’ll also need to upload a copy of the notice of deficiency and complete a separate Statement of Taxpayer Identification Number. Do not put your Social Security number anywhere in the petition itself; it goes only on that separate form.
The filing fee is $60, payable online, by check, or by money order made out to “Clerk, United States Tax Court.”9United States Tax Court. Court Fees If you can’t afford it, you can apply for a fee waiver. Petitions can be filed electronically through DAWSON 24 hours a day, and an electronic petition must be received by 11:59 p.m. Eastern Time on the last day of the deadline.10United States Tax Court. How to eFile a Petition Do not file both electronically and by mail.
Small Tax Case Procedures
If the total amount in dispute (including penalties) is $50,000 or less for any single tax year, you can ask the Tax Court to hear your case under simplified “small case” procedures.11Office of the Law Revision Counsel. 26 USC 7463 – Disputes Involving $50,000 or Less These cases are designated with an “S” and involve less formal rules of evidence, shorter hearings, and a more conversational process. Most self-represented taxpayers choose this option. The tradeoff: a small case decision cannot be appealed by either side, and it doesn’t set precedent for other cases.
Other Ways to Respond
A Tax Court petition isn’t your only choice. Depending on your situation, one of the following paths may make more sense.
Agree with the IRS
If you review the notice and conclude the IRS got it right, the fastest resolution is to sign and return the enclosed Form 870 (Waiver of Restrictions on Assessment). Signing lets the IRS immediately assess the tax and ends the dispute, which also stops additional interest from piling up during a drawn-out process.12Internal Revenue Service. Form 870 – Waiver of Restrictions on Assessment and Collection of Deficiency in Tax Once you sign, you give up your right to petition Tax Court on these issues for that tax year.
Pay First, Then Sue for a Refund
If you’d rather have your case heard by a U.S. District Court or the U.S. Court of Federal Claims, you can pay the full proposed deficiency and then file a claim for refund using Form 1040-X. If the IRS denies the refund or doesn’t act on it within six months, you can file a refund lawsuit. This route requires more money up front, but some taxpayers prefer it for the jury trial option in District Court or because legal precedent in their circuit is more favorable.
Request Audit Reconsideration
In limited situations, you may be able to request an audit reconsideration rather than going to court. This is most relevant if you never responded to the original audit because you didn’t receive the correspondence, or if you have new documentation the IRS hasn’t seen.13Taxpayer Advocate Service. Audit Reconsiderations Audit reconsideration does not extend the 90-day petition deadline, so if you go this route, protect yourself by filing a Tax Court petition at the same time. The IRS can rescind the notice of deficiency with your consent if the reconsideration resolves the issue, which effectively resets the process.6Office of the Law Revision Counsel. 26 U.S. Code 6212 – Notice of Deficiency
Innocent Spouse Relief
If the deficiency stems from a joint return and your spouse or former spouse is responsible for the errors, you may be eligible for innocent spouse relief by filing Form 8857. This is a separate process from the Tax Court petition, but the 90-day deadline for petitioning Tax Court still applies to the underlying deficiency. Filing the petition protects your rights while the innocent spouse claim is evaluated.
If You Agree but Can’t Afford to Pay
Owing the tax and being unable to write a check for the full amount are two different problems, and the IRS has procedures for the second. After the deficiency is assessed, you can request an installment agreement to pay over time. For balances of $50,000 or less in combined tax, penalties, and interest, you can apply online. For larger amounts, you’ll need to submit Form 9465 and possibly Form 433-F detailing your financial situation.14Internal Revenue Service. Payment Plans; Installment Agreements
While an installment agreement is pending or in effect, the IRS is generally prohibited from levying your assets. Interest continues to accrue on the unpaid balance, so you’ll pay more over time than you would with a lump sum, but the agreement prevents more aggressive collection actions. If your financial situation is genuinely dire, an offer in compromise, where the IRS agrees to accept less than the full amount, may also be an option, though qualifying is difficult.
What Happens If You Ignore the Notice
If 90 days pass without a Tax Court petition or a signed Form 870, the IRS assesses the full proposed deficiency as final. At that point the amount becomes an official debt on your account, and the IRS begins its collection process with demand notices.15Internal Revenue Service. Understanding Your CP504 Notice
If you still don’t pay or make arrangements, the IRS can file a Notice of Federal Tax Lien, a public record establishing the government’s claim against your property. A tax lien damages your credit and makes it difficult to sell real estate or borrow money. Beyond liens, the IRS can issue levies to seize wages, bank accounts, Social Security benefits, and other assets.16Internal Revenue Service. What’s the Difference Between a Levy and a Lien A lien is a legal claim; a levy is an actual seizure.
Even after the assessment becomes final, you still have the pay-and-sue option. You can also request a Collection Due Process hearing when you receive a lien or levy notice, which temporarily halts enforcement. None of these later options are as favorable as responding within the original 90-day window, where you get to challenge the tax in court without paying a dime up front.