TAX FORMS · IRS · BUILT IN
Add the original return, the corrected forms, the client’s email and your worksheet. Fyllyo fills Form 1040-X on your Mac. Any amount the documents disagree on is left for you, with the reason.
Most of Form 1040-X is three columns of numbers: the original return, the change and the corrected amount. The documents behind them rarely agree line by line, and the totals depend on each other. These are the common places AI tools and autofill get it wrong. What the form requires is for the IRS to say. Follow its instructions. IRS instructions for Form 1040-X.
A worksheet or email can give both a net change and a corrected amount, and a typo can make them disagree. Software that copies both can fill a line where the original plus the change isn’t the corrected amount, and every total below it inherits the error.
A W-2c shows “previously reported” and “correct” amounts for one employer. Software can copy the previously reported figure into the original-amount column, though the original return combined every W-2.
Form 1040-X has a dozen lines that are sums or differences of other lines. A language model asked for the totals can get the arithmetic wrong, or copy a total from a worksheet that has its own mistake.
The same payment can show up on the original return, in the client’s email and on a worksheet. Software can count an estimated payment as tax paid with the return too.
Return copies and W-2s often show an SSN as XXX-XX-6218. Copied into the form, that’s an invalid number in a required box.
The original return’s list of dependents looks like an answer to copy, but Part I of Form 1040-X is about dependents being added or removed.
The original return shows the Identity Protection PIN used that year. The IRS issues a new one every year, so a PIN copied from the old return can be the wrong one.
With a test client and four documents (the 2024 return as filed, a W-2c, the client’s email and the preparer’s worksheet, which had one transposed number), Fyllyo filled 46 fields in 27 seconds. It left 8 for the preparer, each with the reason.
A test client’s 2024 amendment, from four documents. Fyllyo fills 46 fields in under a minute and leaves the one amount the documents disagree on for the preparer. Then the form is saved and signed.
Fyllyo fills 126 of the 127 fields on Form 1040-X from the client’s documents. Lines the documents don’t support stay blank and are listed for you to check.
You do
You confirm on every form
Fyllyo reads the documents you already have. These can be PDFs, scans, photos, Word files or typed notes, and you can add several at once. Fyllyo works out which document answers which line.
Client documents and the filled form never leave your computer. Fyllyo uploads nothing. Once it is set up, filling works offline.
Fyllyo doesn’t decide whether a return should be amended, give tax advice or e-file. Use the IRS’s instructions for Form 1040-X and your professional judgement. Fyllyo does the reading and the typing.
The built-in form is the February 2024 revision, for amending 2024 returns. For another year, add that year’s fillable 1040-X from the IRS as your own form. You set it up once, then fill it like this one. Set up that fillable PDF as your own form →
Fyllyo reads scans and photos as well as PDFs, Word files and typed notes. Clear, readable copies give the best results, and every answer still shows the line it came from.
Try form filling free for 5 days. Then buy Fyllyo Paid once for $99. It is a lifetime licence with free updates and no subscription. Filling forms on your Mac uses no AI credits. Pricing and licence details.
fyllyo