What this IRS notice code means, and what to check before you reply.
Start with these steps before you reply.
Read the notice carefully and note any deadline. Gather returns, notices, and payment records. Book a free strategy session before responding if the amount is large, unclear, or collection language appears.
We didn’t allow the amount claimed as employee business expenses on page 1 of your tax return. Expenses from Form 2106, Employee Business Expenses, must be claimed as an itemized deduction on Schedule A, Itemized Deductions. If you filed a Schedule A, we changed it to include these expenses. If you did not file a Schedule A and your employee business expenses were: - less than the standard deduction, we did not allow them as a deduction from your income. - greater than the standard deduction after subtracting the 2% AGI limitation, we allowed them as an itemized deduction on Schedule A because it lowered your taxable income. Note: If you have other itemized deductions in addition to the business expenses, you may file Form 1040X, Amended US Individual Income Tax Return, and include them on Schedule A, Itemized Deductions, to reduce your tax.
166 is in our IR Manual catalog. Official wording is dense — we translate it for business owners and individuals and map realistic next steps.
Every notice in this library, sorted the way the IRS numbers them.