What Triggers an IRS Audit? DIF and Information Matching

People imagine an auditor with a red pen. In reality, most federal selection starts with automated scoring and information matching. Understanding DIF (Discriminant Function) and document matching helps you file a return that lines up with what payers already reported to the IRS.

TL;DR

DIF is a confidential scoring system; you cannot see your score. High scores can mean human review.
Information matching compares your return to W-2, 1099, K-1, and other data; mismatches can produce CP2000 notices or referrals.
Large deductions relative to income and repeat inconsistencies raise risk.
Accuracy (every line tied to a document) is your best practical defense.

What DIF is (and is not)

The IRS uses historical audit results to train models that flag unusual combinations of deductions, credits, and income. DIF is not public. Speculating about “the formula” is less useful than asking: “Would my return look normal if I were comparing it to my own 1099s?”

Returns with high DIF scores may go to a human reviewer who decides whether to open an exam.

Information matching: the IRS already has your W-2

Before DIF matters, the IRS often knows:

Wages from Form W-2
Interest from 1099-INT
Dividends from 1099-DIV
Stock sales from 1099-B (proceeds and often basis)
Self-employment and gig income from 1099-NEC and 1099-K

If your return omits a form the IRS received, you may get a CP2000 or similar notice. That is not a “random audit”; it is document matching.

Common human-audit themes (after automation)

Examiners still work cases where:

Schedule C expenses look high relative to gross receipts.
Charitable contributions lack appraisal or receipt rules for large gifts.
Rental losses fail passive activity tests.
Foreign accounts trigger FBAR/8938 questions when applicable.

Worked example: the “missing 1099”

You reported $95,000 wages. Two W-2s totaling $110,000 were filed with the IRS. You will likely get a notice proposing $15,000 of extra wages. The fix is not arguing; it is proving whether one W-2 was duplicate, wrong, or belongs to a spouse.

Document proof callout: Keep all W-2s and compare Box 1 sum to Line 1 of Form 1040 before you file.

FAQ

Is there a published DIF score threshold?
No.

Do rich people get audited more?
Higher income correlates with more complex returns and sometimes higher exam rates; your focus should be documentation.

Can I avoid audits completely?
No. You can reduce mismatch risk by reconciling all income documents.

How to act on this today

Before you worry about DIF, run information matching yourself: verify your return against W-2s and 1099s in BasilTax, then sign up to keep that workflow every year.

Educational content only—not individualized tax advice.