Form 941 to W-2 Reconciliation
The IRS matches the amounts on your four quarterly Forms 941 against your Form W-3 totals every year. When they don't agree, you get a letter with a 45-day response window.
Reconciliation isn't optional housekeeping. It's a matching program run against every employer, every year, and the notices carry penalties.
The quarterly filing schedule
| Quarter | Covers | Due |
|---|---|---|
| Q1 | January-March | April 30 |
| Q2 | April-June | July 31 |
| Q3 | July-September | October 31 |
| Q4 | October-December | January 31 |
If you made timely deposits in full payment for the quarter, you may file by the 10th day of the second month following quarter end.
What has to tie
| Item | Form 941 | Form W-2 |
|---|---|---|
| Compensation | Line 2 | Box 1 |
| Federal income tax withheld | Line 3 | Box 2 |
| Social Security wages | Line 5a | Box 3 |
| Social Security tips | Line 5b | Box 7 |
| Medicare wages | Line 5c | Box 5 |
The IRS publishes a year-end reconciliation worksheet with this mapping. One caution: the worksheet still on the IRS site contains tax-computation factors reflecting the 2011-2012 employee payroll tax holiday. The wage mappings are current; the arithmetic on that worksheet is not.
The rates and thresholds
| Rate | Wage base | |
|---|---|---|
| Social Security | 6.2% employee + 6.2% employer | 2025: $176,100 · 2026: $184,500 |
| Medicare | 1.45% each side | No cap |
| Additional Medicare Tax | 0.9%, employee only | Withhold above $200,000 paid |
Three points on Additional Medicare Tax that generate questions every year:
- There is no employer match. It's 0.9% on the employee only.
- You apply the $200,000 threshold uniformly, without regard to the employee's filing status or wages from another employer.
- You cannot stop withholding at an employee's request because they expect a joint return to change the outcome. They reconcile it on their own return.
Why Box 1 doesn't equal Box 3 and Box 5
This is the single most common structural difference, and it is not an error:
401(k) and 403(b) elective deferrals are excluded from Box 1 but included in Boxes 3 and 5. Deferrals escape income tax but remain subject to Social Security and Medicare tax.
Also worth knowing:
- Group-term life over $50,000 is included in Box 1 and Boxes 3 and 5.
- Third-party sick pay requires the Box 13 checkbox and corresponding treatment on the W-3.
- Tips appear in Box 7 as Social Security tips; Box 5 is Medicare wages and tips, with tips folded in rather than broken out.
What happens when they don't match
The IRS runs a Combined Annual Wage Reporting program comparing federal income tax withheld, Medicare wages, Social Security wages and Social Security tips between your employment tax returns and the wage records held by the Social Security Administration.
Two letters:
Letter 99C - issued when the IRS side shows a discrepancy. The review cycle begins each April covering the second preceding tax year. 45 days to respond. No response closes the case and the additional tax stands.
Letter 98C - issued when Social Security or Medicare wages reported on Forms W-2 are lower than what you reported on employment tax returns. Also 45 days. Penalties referenced include an intentional-disregard penalty of 10% of the aggregate difference between the returns and the W-2s.
A notice you should not confuse with these: CP2100 and CP2100A relate to Forms 1099 with payee name/TIN mismatches, triggering B-notices and 24% backup withholding. Different program, different forms, different response. Issued twice a year.
For genuine discrepancies arising from mergers, acquisitions or consolidations, Schedule D (Form 941) exists specifically to explain them.
Deposit rules and penalties
| Days late | Penalty |
|---|---|
| 1-5 calendar days | 2% |
| 6-15 calendar days | 5% |
| More than 15 days | 10% |
| Not paid within 10 days of first notice | 15% |
The tiers don't stack. A deposit 20 days late is 10%, not 2 + 5 + 10.
Deposit schedule basics: monthly depositors deposit by the 15th of the following month; the semiweekly schedule is triggered when lookback-period taxes exceed $50,000; and accumulating $100,000 or more in employment taxes on any day requires a deposit by the next business day.
Corrections: Form 941-X
| Situation | Deadline |
|---|---|
| Overreported tax | 3 years from filing or 2 years from payment, whichever is later |
| Underreported tax | 3 years from filing |
Note the deeming rule: Forms 941 for a calendar year are treated as filed on April 15 of the following year if filed before that date.
For underreported amounts, file by the due date of the return for the period in which you discovered the error and pay at the same time - that produces an interest-free adjustment. The protection is lost if the issue was previously examined or the underreporting was knowing.
There are two routes on the form - the adjustment process and the claim process. The claim process is required when filing within 90 days of the limitation period expiring.
Frequently asked questions
Should Box 1 equal Box 3?
Usually not. Retirement plan deferrals reduce Box 1 but not Boxes 3 and 5.
What triggers a mismatch letter?
The IRS matching your four 941s against your W-3. Letter 99C and Letter 98C are the two notices; both give 45 days.
Is CP2100 the same thing?
No. That's a 1099 payee name/TIN mismatch, unrelated to W-2 reconciliation.
Does the employer match Additional Medicare Tax?
No. It's employee-only, 0.9%, withheld above $200,000 paid.
How late is too late to correct a 941?
Three years from filing for underreported tax; three years from filing or two from payment for overreported.
Do the deposit penalty tiers add up?
No. One tier applies, based on how late the deposit was.
This guide is general information about reporting requirements, not legal advice. Verify current deadlines, thresholds and penalty amounts against the issuing agency before you file.