How the IRS Actually Works: Structure, Audits, and Enforcement

The Internal Revenue Service is the most powerful financial institution most Americans interact with — and also one of the least understood. People know the IRS collects taxes, but few understand how it’s organized, how it selects returns for audit, or what happens when you can’t pay your tax bill. This guide pulls back the curtain on the agency that processes over ~150 million individual tax returns each year.

Data Notice: Tax figures and rules cited in “How the IRS Actually Works: Structure, Audits, and Enforcement” are projected 2026 values based on IRS guidance and current legislation. Tax law changes frequently through legislation, regulation, and inflation adjustments. Verify all figures with IRS.gov and consult a qualified tax professional. [how-irs-works]

What the IRS Does

The IRS is a bureau within the U.S. Department of the Treasury. Its primary responsibilities include:

Collecting federal taxes — Individual income tax, corporate income tax, payroll taxes, estate taxes, excise taxes, and gift taxes
Processing tax returns — Over ~150 million individual returns and tens of millions of business returns each year
Enforcing tax laws — Conducting audits, collecting unpaid taxes, and investigating tax fraud
Issuing refunds — Sending back overpayments to taxpayers (the IRS issues over ~$300 billion in refunds annually)
Providing taxpayer assistance — Phone support, walk-in centers, online tools, and publications

The IRS does not write tax laws. Congress creates and changes tax law (like the One Big Beautiful Bill). The IRS’s job is to implement and enforce whatever Congress passes.

IRS Leadership and Structure

The Commissioner

The IRS is led by the Commissioner of Internal Revenue, who is appointed by the President and confirmed by the Senate for a five-year term. The Commissioner sets priorities, manages operations, and testifies before Congress.

The Four Operating Divisions

The IRS is organized into four main operating divisions, each focused on different types of taxpayers:

1. Wage and Investment (W&I)

Serves: Individual taxpayers whose income is primarily from wages and investment income — roughly 120+ million returns per year.

This is the division most Americans interact with. W&I handles:

Processing individual tax returns (Form 1040)
Issuing refunds (track yours with the IRS refund tracker)
Administering credits like the EITC and Child Tax Credit
Operating the toll-free help line
Managing the IRS Free File program and Volunteer Income Tax Assistance (VITA)

2. Small Business/Self-Employed (SB/SE)

Serves: Small business owners, self-employed individuals, and partnerships with assets under ~$10 million — approximately 57+ million returns.

SB/SE handles:

Schedule C filers and small business returns
Self-employment tax matters
Payroll tax compliance for small employers
Estate and gift tax returns
Most individual audits (since many involve small business income)

3. Large Business and International (LB&I)

Serves: Corporations, partnerships, and other businesses with assets of ~$10 million or more, plus international tax matters.

LB&I handles:

Corporate tax compliance for large companies
Transfer pricing and international tax issues
Tax treaty interpretation
Offshore compliance programs

4. Tax Exempt and Government Entities (TE/GE)

Serves: Nonprofits, charities, pension plans, and government entities.

TE/GE handles:

501(c)(3) determinations (deciding whether organizations qualify as tax-exempt)
Compliance for employee benefit plans (401(k)s, pensions)
Tax-exempt bond oversight
Government entity compliance

Other Key Offices

Criminal Investigation (CI) — The IRS’s law enforcement arm. CI investigates tax fraud, money laundering, and financial crimes. CI special agents carry badges and firearms and can make arrests.
Office of Chief Counsel — The IRS’s legal division, providing legal advice and representing the IRS in Tax Court.
Taxpayer Advocate Service (TAS) — An independent organization within the IRS that helps taxpayers resolve problems. More on this below.
IRS Independent Office of Appeals — Handles disputes between the IRS and taxpayers before cases go to court.

IRS Processing Centers

The IRS operates several processing centers across the country that handle the physical and digital flow of tax returns:

Submission Processing Centers — Located in Austin (TX), Kansas City (MO), and Ogden (UT). These centers receive, sort, and process paper returns. They also process electronically filed returns and handle correspondence.
Campus Operations — Each center employs thousands of workers who open mail, enter data, resolve discrepancies, and process refunds. During peak season (January through April), the IRS brings on tens of thousands of temporary workers.
Electronic Filing — Over ~90% of individual returns are now filed electronically, significantly reducing processing time. E-filed returns are typically processed within ~21 days, while paper returns can take 6+ weeks.

You can manage many interactions with the IRS without calling or mailing anything through your IRS Online Account.

How the IRS Selects Returns for Audit

The word “audit” strikes fear into many taxpayers, but understanding how the process works makes it far less intimidating.

Audit Rates

The overall audit rate for individual taxpayers is quite low — roughly ~0.4% of all returns in recent years. However, the rate varies dramatically by income level:

Income Level	Approximate Audit Rate
Under ~$25,000	~0.4% (higher for EITC claims)
~$25,000 – ~$200,000	~0.2%–0.3%
~$200,000 – ~$500,000	~0.4%–0.6%
~$500,000 – ~$1 million	~0.7%–1.0%
Over ~$1 million	~1.0%–2.0%
Over ~$10 million	~5%–10%+

How Returns Are Selected

The IRS uses several methods to identify returns for audit:

The DIF Score

The most important selection tool is the Discriminant Information Function (DIF) score. The IRS runs every return through a computer model that compares your return to statistical norms for taxpayers with similar income and filing characteristics. The model assigns a score based on the probability that an audit will result in additional tax.

Returns with high DIF scores are flagged for human review. An experienced IRS classifier then examines the return and decides whether to pursue an audit and which items to examine.

The IRS keeps the exact DIF formula secret to prevent gaming, but common triggers include:

Unusually high deductions relative to income
Large Schedule C losses, especially recurring ones
Significant discrepancies between reported income and W-2s / 1099s on file
Round numbers on deductions (suggesting estimates rather than actual amounts)
Home office deductions
Large charitable contributions relative to income

Document Matching

The IRS’s Automated Underreporter (AUR) program matches the income reported on your return against the information returns (W-2s, 1099s) that payers submit. If your employer reported paying you $75,000 but you only reported $65,000, the system will catch it and generate a CP2000 notice.

This isn’t technically an audit — it’s a proposed adjustment. But it’s the most common way the IRS catches unreported income.

If your business partner, employer, or investor is being audited, the IRS may audit your return as well to verify related transactions.

Random Selection

A small number of returns are selected randomly through the National Research Program (NRP) to gather data about compliance patterns. These audits tend to be more thorough.

Informant Tips

The IRS receives tips from whistleblowers and ex-spouses. For cases involving over ~$2 million in dispute, the IRS Whistleblower Office may pay informants 15%–30% of the collected proceeds.

Types of Audits

Not all audits are created equal. There are three main types:

Correspondence Audit

The most common type (~75% of all audits). The IRS sends you a letter asking you to verify specific items on your return — usually a deduction or credit. You respond by mail with supporting documentation. You never meet an IRS agent in person.

Office Audit

You’re asked to bring documentation to a local IRS office and meet with an examiner in person. These focus on specific issues but are more detailed than correspondence audits.

Field Audit

An IRS revenue agent visits your home or place of business to examine your records. These are the most thorough and are typically reserved for complex returns, high-income individuals, and businesses. Field audits can take months.

What Happens If You Owe and Can’t Pay

If you file your return and owe more than you can pay, the IRS has a structured collection process. The key principle: always file your return, even if you can’t pay. The penalty for not filing is far worse than the penalty for not paying.

The Collection Timeline

Notice and demand — The IRS sends a bill (typically a CP14 notice) showing the amount owed plus interest and penalties
Follow-up notices — If you don’t pay or respond, the IRS sends increasingly urgent notices (CP501, CP503, CP504)
Final Notice of Intent to Levy — A CP504 or Letter 1058 is the last warning before the IRS can seize assets
Levy and lien — The IRS can file a tax lien (a legal claim against your property) or levy (seize) your bank accounts, wages, or other assets

Options If You Can’t Pay in Full

Short-term payment plan — If you can pay within 180 days, you can set up a short-term plan with no setup fee
Installment agreement — Monthly payments over up to 72 months. You can apply online through your IRS Online Account for balances under ~$50,000
Offer in Compromise (OIC) — A deal to settle your tax debt for less than you owe. The IRS accepts these when there’s doubt about collectibility or the amount owed. Acceptance rates are low (~30%–40%) and the process takes 6–12+ months
Currently Not Collectible (CNC) — If you can demonstrate that paying would create an economic hardship, the IRS can temporarily halt collection. Interest and penalties still accrue
Penalty abatement — If you have a clean compliance history, you can request removal of failure-to-file or failure-to-pay penalties through “first-time penalty abatement”

The Taxpayer Advocate Service

The Taxpayer Advocate Service (TAS) is an independent organization within the IRS that helps taxpayers who:

Are experiencing economic harm or are about to suffer economic harm
Have been unable to resolve their issue through normal IRS channels
Face a systemic problem that the IRS hasn’t fixed

The TAS is led by the National Taxpayer Advocate, who reports directly to Congress with an annual report identifying the most serious problems taxpayers face.

How to Contact the TAS

Call 1-877-777-4778
Visit a local Taxpayer Advocate office (there’s at least one in every state)
Submit Form 911 (Request for Taxpayer Advocate Service Assistance)

The TAS is free and can be invaluable when you’re stuck in the IRS bureaucracy.

IRS Taxpayer Bill of Rights

Every taxpayer has fundamental rights when dealing with the IRS. The Taxpayer Bill of Rights includes:

The right to be informed — You’re entitled to clear explanations of tax laws and IRS procedures
The right to quality service — The IRS should provide prompt, courteous, and professional assistance
The right to pay no more than the correct amount of tax — Including interest and penalties
The right to challenge the IRS’s position and be heard — You can provide documentation and disagree with findings
The right to appeal an IRS decision — Through the Independent Office of Appeals
The right to finality — You have the right to know the maximum time for challenging your tax position
The right to privacy — IRS inquiries and enforcement must be no more intrusive than necessary
The right to confidentiality — The IRS cannot disclose your information without authorization
The right to retain representation — You can hire a tax professional to represent you
The right to a fair and just tax system — Including relief from penalties when acting in good faith

IRS Budget and Staffing

The IRS’s ability to serve taxpayers and enforce the law depends on its funding:

Budget: The IRS’s annual budget has fluctuated significantly. The Inflation Reduction Act of 2022 provided ~$80 billion in additional funding over 10 years, though subsequent legislation has clawed back portions of that funding.
Staffing: The IRS employs roughly ~80,000–90,000 full-time equivalent workers — significantly fewer than its peak staffing levels despite a growing population and increasingly complex tax code.
Technology: The IRS is in the process of modernizing decades-old IT systems. Many core systems still run on code written in the 1960s and 1970s. Modernization efforts include online accounts, digital document upload, and improved phone systems.

The IRS processes more than ~$4.7 trillion in tax payments annually, making it one of the most efficient revenue collection agencies in the world — collecting roughly ~$12 for every $1 of budget.

Frequently Asked Questions

What triggers an IRS audit?

The most common triggers are high DIF scores (statistical outliers), document mismatches between your return and your W-2s/1099s, large deductions relative to income, and claiming certain credits like the EITC. However, the overall audit rate is very low — less than ~0.5% for most income levels.

How far back can the IRS audit?

Generally, the IRS can audit returns from the past 3 years. If they find a substantial error (underreporting income by more than 25%), the window extends to 6 years. There is no time limit for cases involving fraud or failure to file.

Can I represent myself in an audit?

Yes. For correspondence audits, you simply respond with documentation. For office or field audits, you can bring a representative — a CPA, enrolled agent, or tax attorney. If the audit results in a dispute, you can appeal to the IRS Independent Office of Appeals or petition the U.S. Tax Court.

Does the IRS accept payment plans?

Yes. For balances under ~$50,000, you can set up an installment agreement online. Larger balances may require financial disclosure forms. Interest and penalties continue to accrue during the payment plan, but the IRS won’t levy your property while you’re in compliance with the agreement. Apply through your IRS Online Account.

How do I check on my refund?

Use the IRS “Where’s My Refund?” tool at irs.gov or the IRS2Go mobile app. You’ll need your Social Security number, filing status, and exact refund amount. See our IRS Refund Tracker guide for details.

Is the IRS really going to hire 87,000 new agents?

This figure has been widely mischaracterized. The Inflation Reduction Act funding was intended to hire across all IRS functions — customer service, IT modernization, compliance, and processing — over a 10-year period, with many hires replacing retiring workers. The actual number and mix of new hires depends on annual appropriations and ongoing budget negotiations.

This article about how the irs actually works: structure, audits, and enforcement provides general tax education and is not a substitute for professional tax advice. Laws and regulations discussed here may have changed since publication. Work with a licensed tax advisor for decisions affecting your specific tax situation.