Catch tax-return mistakes before you hit submit. 50+ checks covering W-2/1099 reconciliation, deduction documentation, credit eligibility, retirement contribution verification, and common 2026 traps.
Most tax-return mistakes are not 'wrong math' — they're missed items: a 1099 you forgot you'd get, a deduction you didn't itemize, a credit you didn't claim, a contribution limit you exceeded. This checklist runs through the categories where mistakes cluster, so you catch them BEFORE you sign and submit (where they're either expensive to fix or just permanently lost).
The checklist is organized by category: income reconciliation (W-2s match year-end paystub? 1099-DIV / 1099-INT / 1099-B from every brokerage? K-1 from any partnership/S-corp? Backup withholding correctly captured?), deductions (standard vs. itemized run both ways? SALT cap respected? Mortgage interest only on first $750k of debt?), credits (CTC eligibility for each child? Saver's Credit? Energy credits for any home improvements? Education credits?), retirement (401(k) limit met but not exceeded? IRA contribution within deadline?), state-specific (state-specific deductions and credits that federal-only software might miss?).
Plus 2026-specific items: OBBBA provisions (Trump tax cuts permanence), changes to SALT cap, Roth catch-up requirements for high earners, and the SECURE 2.0 super catch-up for age 60-63 ($11,250 instead of $8,000).
Step 1 — Walk through each category. Income, deductions, credits, retirement, state-specific, 2026-specific. Each category has 8-12 specific check items.
Step 2 — Flag items that need follow-up. Mark which items apply, which don't, which need more research. The checklist saves your progress so you can return.
Step 3 — Resolve before filing. Each flagged item links to the source IRS guidance (publication or form instruction). Resolve, mark done, move to next.
Walk through 50+ items by category. Each item flags whether it applies to your filing situation and links to the source IRS guidance. Skip the items that don't apply.
Open the checklist →Missing 1099 forms — especially 1099-INT from minor savings accounts, 1099-B from old brokerage accounts, and 1099-NEC from gig work. The IRS receives the 1099 even when you don't (or didn't keep the paper copy), so missing one triggers an automated CP2000 notice 12-18 months later proposing an underpayment + interest + sometimes penalty. Always log into every financial account and download the tax docs before filing.
Run both. For 2026: standard deduction is $30,000 MFJ / $15,000 single / $22,500 HoH. Itemize only if your SALT (capped at $10k) + mortgage interest (on up to $750k of acquisition debt) + charitable contributions + medical (over 7.5% of AGI) total exceeds the standard deduction. After 2017 TCJA, ~90% of households take the standard deduction; itemizing pays off mainly for high-mortgage homeowners and large charitable givers.
IRA (traditional and Roth): April 15 of the following year, no extensions. So 2026 IRA contributions are due April 15, 2027. 401(k), 403(b), 457(b): contributions must be made by Dec 31 of the tax year — no after-year-end window for employee deferrals. HSA: April 15 of following year (same as IRA). SEP-IRA: tax-filing deadline including extensions (Oct 15 if you file an extension). Solo 401(k): generally Dec 31 for employee portion, tax-filing deadline for employer portion.
Dec 31 of the tax year. Roth conversions count in the tax year they happen, NOT the year following (unlike IRA contributions). So a conversion done Dec 31, 2026 = taxed on your 2026 return. A conversion done Jan 1, 2027 = on your 2027 return. Plan accordingly: if you want to lock in low-bracket year 2026 conversions, the conversion must execute on or before Dec 31, 2026. Trustees can be slow in late December — give yourself a 2-3 week buffer.