When the IRS disallows tax deductions on your return, you owe the tax you would have paid without them, plus interest running from the original due date, and often a penalty on top. You are not stuck with that result. Federal law gives you a structured path to push back: first through the IRS Independent Office of Appeals, and if that fails, in United States Tax Court before you have to pay the disputed amount.
Why the IRS Disallows a Deduction
Most disputes start with a single question: was the expense ordinary and necessary for your business? That standard comes straight from the Internal Revenue Code, which allows a deduction only for expenses that are common in your industry and helpful to running the business.1Office of the Law Revision Counsel. 26 USC 162 – Trade or Business Expenses Examiners regularly reject deductions where personal and business spending blur together. A whole phone bill, all your home utilities, or a vehicle you also use for personal errands, claimed without clear business-use records, is one of the fastest ways to lose a deduction.
Hobby Losses
If a side business consistently loses money, the IRS may treat it as a hobby. The tax code presumes an activity is for profit if it produces income exceeding its expenses in at least three of the last five tax years, or two of seven years for horse breeding and racing.2Office of the Law Revision Counsel. 26 USC 183 – Activities Not Engaged in for Profit Failing that test doesn’t end the matter, but it removes the presumption and forces you to prove profit motive through your business plan, expertise, and time invested.3Internal Revenue Service. Is Your Hobby a For-Profit Endeavor Once the activity is reclassified as a hobby, deductions are capped at the income the activity produced. Losses cannot offset wages, investment returns, or other income.
Fines, Penalties, and Illegal Payments
You cannot deduct amounts paid to a government entity in connection with a law violation or an investigation into one.1Office of the Law Revision Counsel. 26 USC 162 – Trade or Business Expenses That covers OSHA fines, environmental penalties, and traffic tickets from business driving. A narrow exception exists for amounts that a court order or settlement specifically identifies as restitution, or as payment to come into compliance with the law, but calling something restitution isn’t enough. You must show the payment compensated for harm rather than punishing wrongdoing.
What a Disallowed Deduction Actually Costs
The tax owed is only the starting figure. The IRS charges interest on any underpayment from the original due date of the return, compounded daily. For the first half of 2026, the underpayment rate is 7 percent for January through March and 6 percent for April through June, calculated as the federal short-term rate plus three points.4Internal Revenue Service. Quarterly Interest Rates On a deficiency that spans several years, that interest alone gets serious.
The 20 Percent Accuracy Penalty
If the IRS decides the underpayment came from negligence, a substantial understatement of income, or a significant overstatement of deductions, it adds a penalty of 20 percent of the underpayment.5Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments Negligence here means you didn’t make a reasonable attempt to comply with the law or keep adequate records. This penalty stacks on the tax and interest.
The 75 Percent Civil Fraud Penalty
When the IRS establishes that any part of your underpayment was due to intentional fraud, the penalty on the fraudulent portion is 75 percent.6Office of the Law Revision Counsel. 26 USC 6663 – Imposition of Fraud Penalty Once fraud is proven on any piece of the underpayment, the entire underpayment is presumed fraudulent unless you rebut that presumption by a preponderance of evidence. Fraud also eliminates the normal statute of limitations, so the IRS can pursue the year indefinitely.
The Records That Save a Deduction
Most deduction fights turn on documentation. The tax code requires that travel, meal, and gift expenses be backed by records showing the amount, time and place, and business purpose of each expense.7Office of the Law Revision Counsel. 26 USC 274 – Disallowance of Certain Entertainment, Etc., Expenses Federal regulations describe what that looks like: a log, diary, or expense report capturing each element at or near the time of the expense, supported by receipts showing amount, date, location, and nature of the charge.8eCFR. 26 CFR 1.274-5 – Substantiation Requirements A hotel receipt, for example, needs the hotel name, location, date, and separate lodging and meal charges. Reconstructions from memory months later rarely satisfy an examiner.
Bank and credit card statements are useful backup, showing cash actually left your account on the date and in the amount you claimed. For large purchases like equipment or vehicles, bills of sale and titles help fix the cost basis. Every number on your return should have a matching piece of paper behind it.
When Receipts Are Gone
If your general business receipts are lost, the judicial rule from Cohan v. Commissioner lets the IRS or a court estimate a deduction when you can offer some factual basis for the estimate. It does not apply to travel, meals, and gifts, which are held to the strict substantiation rules above. For those categories, no receipt means no deduction. For other business expenses, expect a smaller number than you originally claimed, because the estimate will lean against the taxpayer who lost the records.
During an audit the IRS sends an Information Document Request, Form 4564, listing exactly which records it wants.9Internal Revenue Service. Form 4564 – Information Document Request Treat it as your checklist. Organize the records by category and date before sending them.
How Long the IRS Has to Come After You
The standard audit window is three years from the date you filed the return.10Office of the Law Revision Counsel. 26 USC 6501 – Limitations on Assessment and Collection After that period closes, the IRS generally cannot assess additional tax. Three exceptions matter:
- If you omit more than 25 percent of the gross income reported on the return, the IRS has six years.10Office of the Law Revision Counsel. 26 USC 6501 – Limitations on Assessment and Collection
- If you filed a fraudulent return with intent to evade tax, or never filed at all, there is no limitations period.
- The IRS can ask you to sign a consent extending the assessment period. You may refuse, or limit the extension to specific issues or a specific timeframe.
If the IRS approaches you near the end of the three-year window and requests an extension, think carefully before signing. Refusing can force the IRS to either issue a notice of deficiency immediately or let the clock expire.
Who Has to Prove What
The default is that you carry the burden of proving your deductions are legitimate. That can shift. If your case reaches court and you introduce credible evidence supporting your position, the burden moves to the IRS, which then has to prove you wrong rather than you proving yourself right.11Office of the Law Revision Counsel. 26 USC 7491 – Burden of Proof The shift requires three things: you substantiated the items, you kept all required records, and you cooperated with reasonable IRS requests during the audit. Partnerships, corporations, and trusts must also meet a net worth threshold. Good record-keeping does more than protect the deduction; it can flip who has to prove what in a courtroom.
Filing an Administrative Appeal
If the examination report concludes you owe more tax and you disagree, the IRS sends a 30-day letter explaining the proposed changes and giving you 30 days to request review by the IRS Independent Office of Appeals.12Internal Revenue Service. Letters and Notices Offering an Appeal Opportunity
The Written Protest
When the total additional tax and penalties exceed $25,000 for any single tax period, you file a formal written protest identifying the findings you disagree with, the facts supporting your position, and the legal arguments for why the deductions should stand. For $25,000 or less per period, a simplified request on Form 12203 does the job.13Internal Revenue Service. 14Internal Revenue Service. Internal Revenue Manual 8.1.1 – Appeals Operating Directives and Guidelines The conference is informal. Many disputes end here with a reduced liability both sides can live with, and this stage is often the most cost-effective place to resolve a fight.
Taking the Case to Tax Court
If Appeals cannot resolve the dispute, the IRS issues a Notice of Deficiency, also called a 90-day letter. This is the formal legal notice that the IRS proposes to assess additional tax.15Taxpayer Advocate Service. 90-Day Notice of Deficiency You then have 90 days from the mailing date, or 150 days if you’re outside the United States, to file a petition with the United States Tax Court.16Office of the Law Revision Counsel. 26 USC 6212 – Notice of Deficiency This deadline is set by statute and cannot be extended. Miss it and the IRS assesses the tax; your only remaining option is to pay in full and sue for a refund in federal district court or the Court of Federal Claims.
Tax Court has a real advantage: you can challenge the determination before paying. The filing fee is $60.17United States Tax Court. Court Fees
Small Tax Case Procedures
When the amount in dispute is $50,000 or less for any single tax year, you can elect the Tax Court’s small case procedures.18United States Tax Court. Case Procedure Rules of evidence are relaxed, the process is faster, and many taxpayers appear without an attorney. The tradeoff is finality: decisions under these procedures cannot be appealed by either side.
Getting a Representative
You don’t have to face this alone, and in many cases you shouldn’t. Three types of professionals have unlimited practice rights before the IRS: attorneys, certified public accountants, and enrolled agents.19Internal Revenue Service. Enrolled Agent Information Any of them can represent you during an audit, at Appeals, or before any IRS office. Enrolled agents earn the designation by passing a three-part IRS exam or through qualifying IRS employment. To authorize a representative, file Form 2848, Power of Attorney and Declaration of Representative.20Internal Revenue Service. Instructions for Form 2848 Once it’s on file, your representative can communicate with the IRS without you present, receive copies of correspondence, and negotiate on your behalf.
Hourly rates vary. Tax attorneys generally charge $300 to $850 per hour, and CPAs handling audit defense generally run $150 to $600 per hour, depending on complexity and market. When the amount at stake is significant, experienced representation often pays for itself because seasoned practitioners know which arguments carry weight at Appeals and how to present evidence efficiently.
If You Don’t Pay
Losing the dispute, or ignoring the notices, doesn’t make the tax go away. The IRS follows a defined escalation. After balance-due notices, the agency sends a CP504, its formal Notice of Intent to Levy, warning that it intends to seize wages, bank accounts, or a state tax refund to satisfy the debt.21Internal Revenue Service. Understanding Your CP504 Notice The IRS may also file a Notice of Federal Tax Lien, which is a public record establishing the government’s priority claim against your property.
Before actually levying assets, the IRS must give you at least 30 days’ written notice and inform you of your right to a Collection Due Process hearing.22Office of the Law Revision Counsel. 26 USC 6330 – Notice and Opportunity for Hearing Before Levy A timely request on Form 12153 generally stops levy action while the hearing is pending and pauses the 10-year collection clock.23Internal Revenue Service. Form 12153 – Request for a Collection Due Process or Equivalent Hearing Miss the 30-day window and you can still request an equivalent hearing within a year, but it does not stop levy action in the meantime and does not preserve your right to challenge the outcome in court. At the hearing, an Appeals Officer will hear alternatives such as an installment agreement or a settlement offer. The costliest mistake taxpayers make at this stage is silence, because enforcement powers are broad and interest and penalties keep compounding while you wait.