Need to Know Tax Income Tax 2026 · Federal & Colorado

Need to Know Tax › Reference

Reference

IRS forms and letters, decoded

A 1099-R is not a 1099-B. A CP504 is not an LT11. This is the cheat sheet for the numbers and letters that show up on your return, in your mailbox, and in conversations with your preparer.

Tax talk is mostly numbers standing in for things. Taxpayers bring in forms they cannot tell apart, the IRS sends a letter with “CP” and three digits in the corner, and the preparer says “your MAGI is over the IRMAA line.” This page is the decoder; where a term has its own article here, the entry is a link.

Forms you receive

These arrive in January and February. Each is matched by computer against your return, which is why a forgotten 1099 produces a CP2000 eighteen months later.

Forms that make up your return

The 1040 is two pages; everything else feeds a line on it. A simple return has three or four schedules; a complicated one can run to twenty.

Forms for dealing with the IRS

Form 8822: the one everyone forgets

The IRS writes to the address on your last return. Move, and every notice goes to the old house, including the one that starts a 90-day clock. A notice mailed to your “last known address” counts as delivered whether you saw it or not. Form 8822 closes the gap: one page, old address, new address, signatures. Colorado residents mail it to the IRS in Ogden, Utah; it takes four to six weeks. No e-filing, no fee.

IRS letters and notices

Every IRS letter has a number in the upper right corner: “CP” for computer notices, “Letter” for ones a person sends, “LT” for automated collection. Three rules: open it, do not ignore it, and show it to your preparer before you answer. Balance-due notices come in order: CP14, CP501, CP503, CP504, then LT11. The IRS never calls, texts or emails first; a call about an “arrest warrant” is a scam.

Business forms

Acronyms and section numbers

The Colorado side

Five more abbreviations show up on a Colorado return. DOR is the Colorado Department of Revenue. DR 0104 is Colorado’s Form 1040; the PN schedule is for part-year residents. TABOR is the Taxpayer’s Bill of Rights, the revenue cap and its refund. PTE is the pass-through entity tax, the SALT-cap workaround for S corporations and partnerships. PERA is the pension for teachers and public employees. On a move, tell Colorado separately, in Revenue Online or on the next DR 0104.

What to bring your preparer

  • Everything with a number on it, including forms that say “this is not a bill”
  • Every IRS letter, before you answer it; the deadline is printed inside
  • The CP01A notice with this year’s IP PIN, for each person on the return who has one
  • Your new address if you moved, so a Form 8822 can go in with the return

Questions people ask

I got a CP2000. Should I file an amended return?

Usually not. Respond on the notice’s own form with a signed statement and the documents; file a 1040-X only if the notice says to. The missing form is almost always a 1099-R rollover, a 1099-B with no basis, or a K-1. A wrong CP2000 that is ignored becomes a CP3219A.

Which notices have a hard deadline?

The LT11, Letter 1058 and CP90: 30 days from the letter date, and the clock does not care that you were traveling. The CP3219A: 90 days to petition the Tax Court, no extensions. The CP14, CP501 and CP503 are bills; answer with payment or a plan.

Open the letter

Keep everything with a number on it. Open the letters; the deadline is printed inside. And if you moved this year, say so before the return is started; Form 8822 takes two minutes and saves a notice you would never have seen.

Published by The Tax Shop, Lone Tree, Colorado

Charles Trautman, EA  ·  taxshop.tax  ·  303-734-1040

Ask a question about this article →

Forms and official pages named in this article

Sources and where to check

Updated October 25, 2026 · tax year 2026 figures

Related