Updated October 16, 2026. Quick answer: Box 4 of Form 1099-K (Rev. December 2026) shows backup withholding, and the form says to include that amount on your income tax return as tax withheld. Boxes 5a to 5l show the gross amount of payment card and third party network transactions for each month of the year. Both are on the recipient copy and keep the same numbers on the March 2024 instructions.
Read box by box from the IRS form text: Form W-2G boxes 9, 11 and 12, Form W-2G slot machine winnings and Form W-2G sports wagering winnings.
What box 4 reports
The recipient copy keeps this box short and says what to do with it: “Shows backup withholding.” “Include this amount on your income tax return as tax withheld.” On the form the box is labelled “Federal income tax withheld”.
Box 4 sits among the other 1099-K boxes explained on the 1099-G and 1099-K boxes guide. It is a different box from the gross-total boxes, because it is the one labelled for tax withheld.
Why a payer would withhold
The recipient copy explains the trigger: “Generally, a payer must backup withhold if you did not furnish your TIN or you did not furnish the correct TIN to the payer.” “See Form W-9, Request for Taxpayer Identification Number and Certification, and Pub. 505.”
The payer instructions describe the same event from the filer’s side: “Enter backup withholding. Persons who have not furnished their TINs to you in the manner required are subject to backup withholding on payments required to be aggregately reported in box 1a.” “A payment made by a TPSO is a reportable payment potentially subject to section 3406 backup withholding.”
The instructions do not put the withholding rate on the form. They refer filers elsewhere: “For more information on backup withholding, including the applicable rate, see part N in Pub. 1099.” The same box appears on other 1099 forms, for example box 4 of the interest and dividend forms in the 1099-INT boxes 4 to 7 page and the 1099-DIV box 4 page.
Boxes 5a to 5l: the monthly amounts
The recipient copy says “Show the gross amount of payment card/third party network transactions made to you for each month of the calendar year.” The payer instructions say “Enter in the appropriate box the gross amount of the total reportable payment transactions for each month of the calendar year.”
| Box | Month printed on the form |
|---|---|
| 5a | January |
| 5b | February |
| 5c | March |
| 5d | April |
| 5e | May |
| 5f | June |
| 5g | July |
| 5h | August |
| 5i | September |
| 5j | October |
| 5k | November |
| 5l | December |
Each monthly box uses the same gross definition as box 1a, so refunds, fees and shipping are not taken out of any month either. The box 1a gross definition is quoted on the box 1a page, and the payer threshold wording is on the 1099-K threshold page.
A worked illustration of the monthly boxes
This is an illustration, not an IRS example. If the first three monthly boxes showed $1,200 in January, $900 in February and $1,100 in March, then $1,200 + $900 + $1,100 = $3,200 for the first quarter of the year. The form does not report a quarterly total; the arithmetic is only a way to line the monthly boxes up with the quarterly dates you use for planning.
For readers who plan around quarterly dates, a first-year walk-through of estimated payments is on the first-year estimated taxes page, and the tax itself is on the self-employment tax page. For the business income itself, the recipient copy points to “If the Form 1099-K is related to your business, see Pub. 334 for more information.”
Where a mismatch usually comes from
Box 4 and the monthly boxes answer different questions, so check them against different records. For box 4, the recipient copy’s own pointers are the Form W-9 and Pub. 505 named above, and the payer is the filer named in the upper-left corner. The form says “If you have questions about the amounts reported on this form, contact the FILER whose information is shown in the upper-left corner on the front of this form.” For the monthly boxes, the dating rule in the gross definition is the one to keep in mind: “The dollar amount of each transaction is determined on the date of the transaction.” A sale is placed in the month of the transaction date, so your own books, if they record sales when money reaches your bank, can differ from the form even when nothing is wrong with either record.
If you also received other 1099 forms for the same year, such as the miscellaneous income form, they are compared on the Form 1099-MISC overview, and the state boxes and the other 1099-K boxes are set out on the 1099-G and 1099-K boxes guide.
State boxes next to them
Right after the monthly boxes the form has the state lines. The recipient copy says “Show state and local income tax withheld from the payments.” Those boxes are separate from box 4, which is the federal amount.
Edition and box numbers
The primary read for this page is the December 2026 revision of Form 1099-K (Copy B, the recipient copy) and the December 2026 Instructions for Form 1099-K, which are the revisions for tax year 2026. Box 4 and boxes 5a to 5l have the same numbers on the March 2024 instructions, which have “Box 4. Federal Income Tax Withheld” and “Boxes 5a Through 5l”. The December 2026 form adds boxes 1c and 1d earlier on the form but does not renumber these. The IRS site was serving the December 2026 revision on 2026-10-16, and the March 2024 revision of the instructions is the previous one. Check the revision printed on the form you received, because the boxes and the payer rules differ between revisions.
Common mistakes
- Ignoring box 4 because the amount is small. The form says “Include this amount on your income tax return as tax withheld.”
- Thinking backup withholding happens only for large sellers. The recipient copy ties it to the TIN: “a payer must backup withhold if you did not furnish your TIN or you did not furnish the correct TIN to the payer”.
- Expecting the monthly boxes to net out refunds. The instructions have each box show “the gross amount of the total reportable payment transactions for each month of the calendar year”.
Related: 1099-INT boxes 4 to 7, 1099-DIV box 4 backup withholding, first-year estimated taxes for the self-employed, self-employment tax explained, and the 1099-K threshold page.
Sources
- Form 1099-K, Payment Card and Third Party Network Transactions (Rev. December 2026), recipient copy: https://www.irs.gov/pub/irs-pdf/f1099k.pdf
- Instructions for Form 1099-K (Rev. December 2026): https://www.irs.gov/pub/irs-pdf/i1099k.pdf
- Instructions for Form 1099-K (Rev. March 2024): IRS archived PDF (irs.gov)
Read from the IRS documents linked above on October 16, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer, the account provider or the IRS is the right place to confirm anything consequential.