How long does the IRS have to complete an audit?

Updated June 23, 2026 by Carolyn Richardson, EA, MBA

You’ve received the dreaded letter from the IRS telling you that your tax return has been selected for audit. “Great,” you think to yourself. “I wonder how long this is going to take?”

We wish we could tell you it will all be over quickly, but the truth is: there’s no single standard timeline for how long an audit will take. What we can talk about is the time limit the IRS generally has to assess additional tax for a given year—because that legal deadline is what often drives how an audit moves.

 

The general rule: Three years to assess additional tax

In most situations, the IRS can assess additional tax within three years after your return was due (including extensions) or—if you filed late—within three years after the IRS received your return, whichever is later. The IRS refers to this deadline as the Assessment Statute Expiration Date (ASED).

 

Exceptions: when the IRS can have more (or unlimited) time

• No return filed: If you don’t voluntarily file a required return, the IRS can assess tax at any time. If the IRS prepares a return for you under the Substitute for Return program, the 3-year limit for assessment generally doesn’t begin until you file your own return.
• Significant underreporting: If you report 25% or less of your income on your return, the time the IRS can assess additional tax generally increases from three years to six years from the date you filed.
• False or fraudulent return: If a false or fraudulent return is filed with intent to avoid tax, the IRS can assess tax for an unlimited amount of time.
• You agree to extend the deadline: During an audit, the IRS may ask you to sign an agreement (often called a consent or waiver) to extend the time to assess tax.
• Some situations can pause (“suspend”) the clock: For example, if the IRS issues a notice of deficiency (a “90-day letter”), the assessment time limit is suspended while you have time to petition the Tax Court and for a period after the case is final.

So…how long will the audit actually take?

Even though the ASED often starts the clock on the IRS’s side, it doesn’t mean your audit will neatly wrap up at a specific month-and-day on the calendar. Audits vary widely based on the issues involved, the type of audit, and how quickly information can be exchanged and reviewed.

If your audit is handled by mail (correspondence audit): the process often feels slow because it’s built around back-and-forth letters. If you can provide complete documentation the first time, that helps. But if the IRS needs follow-up items (or if you discover later that you’ll need to supplement what you sent), the timeline can extend as correspondence is reviewed and responded to.

If your audit is in-person (office or field audit): the start of the audit can move faster because you’re talking directly with the examiner. However, these audits are often used for more complex issues, which can mean more documents, more questions, and more time to reach a conclusion.

 

What if the IRS needs more time? (Extending the statute of limitations)

If the IRS can’t wrap up the examination before the assessment deadline, you may be asked to sign a written agreement to extend the time period for assessment. The IRS describes these written agreements as consents, and they may be for a set amount of time (a fixed date) or, in some cases, they might be open-ended.

Here’s the key point: you can negotiate the proposed extension or refuse to sign. If you don’t agree to extend the deadline, the examiner generally has to make a decision based on the information available at that time—which may not work in your favor if you still need time to gather records. On the other hand, agreeing to a reasonable extension can give everyone time to fully develop the facts, and it can help preserve your opportunity to request an administrative appeal if you disagree with the outcome.

 

Your right to know when it’s over

The IRS’s Taxpayer Bill of Rights includes the right to finality—meaning you have the right to know the maximum amount of time you have to challenge the IRS’s position, the maximum amount of time the IRS has to audit a particular tax year (or collect a tax debt), and when the IRS has finished an audit.

 

What you can do to help the audit go faster
 

• Read every IRS letter carefully and respond by the due date.
• Send complete documentation that directly supports the items being questioned.
• Keep copies of what you send and note when (and how) you sent it.
• If you truly need more time to gather records, ask right away using the contact information in your letter.

If you’re currently under audit and aren’t sure what the IRS is asking for—or you’re worried about deadlines—don’t ignore it. Getting help early can prevent small issues from turning into expensive ones.

 

What if I have audit defense? 

If you have audit defense membership with TaxAudit for the year of your audit, reach out to us right away by clicking here to start a case!