34 — Change in Determining Quantities, Costs, or Valuations Updated for tax year 2025

What this line means

A yes-or-no question asking whether you changed the way you determine inventory quantities, costs, or valuations between this year and last year. If you answer yes, you must attach an explanation describing what changed and why. Most sole proprietors check “No” because they use the same method year after year.

Does this apply to you?

• You carry inventory and completed Part III last year
• You changed your inventory counting method (physical count vs. perpetual system)
• You switched how you assign costs to inventory (FIFO, LIFO, specific identification)
• You changed your valuation method on line 33

Easy to overlook

Answering “yes” triggers an attachment requirement If you check “yes,” the IRS expects a written explanation attached to your return describing exactly what changed. Filing without the attachment can delay processing or prompt a follow-up letter. The explanation does not need to be long — a sentence or two describing the old method, the new method, and the reason for the change is sufficient. ¹ [SOURCE: IRS Schedule C instructions — Part III, Line 34]

Some changes require Form 3115 Certain changes in accounting method — such as switching from FIFO to LIFO or changing your overall inventory valuation method — require filing Form 3115 in addition to checking “yes” here. A simple attachment is not enough for these changes. Consult the Form 3115 instructions to determine whether your change qualifies for an automatic change or requires advance IRS consent. ² [SOURCE: IRS Publication 334 — Tax Guide for Small Business]

Watch out for this

Checking “yes” when you merely corrected a prior-year error rather than making a deliberate method change. Fixing a counting mistake or correcting a math error in your inventory valuation is not a change in method — it is an error correction. Only check “yes” if you intentionally adopted a different approach.

Related lines on your return

• Line 33 — Schedule C — Method used to value inventory; the method this question references
• Line 35 — Schedule C — Inventory at beginning of year; affected by method changes
• Line 42 — Schedule C — Cost of goods sold; the bottom-line number impacted by any change