How do I correct a Form 941 that was filed with an error?

File Form 941-X, a standalone amended return for the specific quarter — one 941-X per quarter corrected. Underreported tax corrected by the due date of the return for the quarter in which you found the error is generally interest-free; overreported tax can be claimed as a refund or as an adjustment credited against current taxes.

Can I just fix a payroll error in the next quarter instead of amending?

Only if the error lives entirely inside the current year's open payroll — for example, a wage misclassification caught before the quarter's 941 is filed, or withholding trued up on a later paycheck in the same year. Once a quarter's 941 is filed with wrong wage or tax figures, the fix for that quarter is a 941-X, not a plug in the next one.

Is there a deadline for filing Form 941-X?

Yes — the general refund limitations period applies: roughly three years from the date the original 941 was filed (returns filed early are treated as filed April 15) or two years from when the tax was paid, whichever is later. Overcollected employee tax also generally requires repaying or obtaining consent from the affected employees first.

Fixing a filed payroll quarter: 941-X versus adjusting forward

A payroll error discovered after the quarter's Form 941 is filed has exactly one correct path: Form 941-X, a standalone amended return for that quarter. The tempting alternative — burying the fix in the next quarter's numbers — corrupts both quarters and guarantees a mismatch when the IRS ties the four 941s to the W-2s. The judgment call is knowing which errors actually require the amendment and which can legitimately be handled in the current period.

When you can fix forward

The quarter isn't filed yet. Reverse and rebook the payroll correctly; the 941 files right the first time. This is why a pre-filing tie-out (see /bookkeeping/payroll-compliance/form-941-basics) is the cheapest correction program that exists.
Same-year withholding true-ups. Under-withheld federal income tax on one paycheck can generally be corrected by withholding more on later paychecks in the same calendar year — the employee's W-2 and the annual totals come out right without touching a filed return, provided the filed quarters' reported figures were accurate for what actually happened.
Deposit timing errors. A late deposit is not a reporting error; there is nothing to amend. The exposure is a failure-to-deposit penalty (see /bookkeeping/payroll-compliance/penalty-notices-payroll), sometimes mitigated by the deposit-application election in the notice procedures or by penalty relief.

When a 941-X is required

Wrong figures on a filed return: unreported wages or bonuses, wages in the wrong tax category, over- or under-withheld Social Security or Medicare, a worker reclassification affecting closed quarters (/bookkeeping/payroll-compliance/employee-vs-contractor), a missed taxable fringe. The mechanics, in concept:

One 941-X per quarter, filed on its own — not attached to a current 941.
Underreported tax corrected by the due date of the 941 for the quarter you discovered the error is an interest-free adjustment under the Section 6205 regulations — pay with the 941-X. Discovery date matters; document it.
Overreported tax can be taken as an adjustment (credited against current liabilities) or a refund claim. For overcollected employee-share taxes you must generally first repay the employee or secure written consent — the certification checkboxes on the form are real requirements, not boilerplate.
Limitations period: about three years from filing (early-filed 941s are deemed filed April 15) or two years from payment, whichever is later.

A discovery procedure

Quantify the error by quarter and by tax (income tax withholding vs Social Security/Medicare behave differently on the form).
Decide the path: forward fix if unfiled or same-year withholding; 941-X otherwise.
Book the correcting journal entries so the ledger's liability accounts agree with the corrected returns (/bookkeeping/payroll-compliance/payroll-journal-entries).
File promptly — the interest-free window and the penalty tiers both reward speed — and diary the related W-2c if one is needed. Publication 15 and the 941-X instructions govern the details.