How to Amend a Tax Return for Kalshi Losses

Yes. You amend a prior year on Form 1040-X, one form per year, and you can generally reach back three years. But for most prediction-market traders the refund comes from claiming a loss you never put on a return, not from the Section 1256 carryback: a carried-back loss offsets only prior-year Section 1256 gains, so an all-losing history recovers nothing that way.

Those are two different moves and almost every write-up on this topic runs them together. This guide separates them, says which one you probably have, shows how far back you can actually go, and is explicit about who gets nothing. It is information, not tax advice. How prediction-market event contracts should be characterized is genuinely unsettled, and the decision is yours and your tax professional's. Federal only; state treatment is named here but not computed.

Can you amend a prior-year return for Kalshi or Polymarket losses?

Yes, if the year is still open, and there are two separate reasons you might want to.

The common one: you never claimed the loss. You traded, you lost, and the loss never appeared on a return, either because you did not report the activity at all or because you reported it as gambling and took the standard deduction, which deducts none of it. Fixing that is a correction to one year, and it needs no winning year anywhere.

The narrow one: the Section 1256 carryback. IRC §1212(c) lets an individual carry a net Section 1256 contracts loss back three years. It is genuinely valuable, and it is useless to most of the people reading this, for a reason covered below.

One thing to get out of the way first, because it is the most common misconception here: you cannot stack several years of losses onto one form. A return covers one tax year, and the IRS instructions for Form 1040-X say to file a separate one for each year you are amending. Three bad years means three amended returns.

How far back can you go?

Under IRC §6511(a), a refund claim has to be filed within three years from the date you filed the return, or two years from the date you paid the tax, whichever is later. Note that the clock runs from when you filed, not from the tax year, so it is not something you can work out from the calendar alone if you extended or filed late.

If you filed early, the IRS treats the return as filed on its due date, and treats withholding and estimated payments as made on that date too. So an early filer gets the same deadline as an April filer, not a shorter one.

For a trader who filed on time each April, the picture in September 2026 looks like this:

Tax year	Original return due	Amend by	Status now
2022	April 18, 2023	April 18, 2026	Closed
2023	April 15, 2024	April 15, 2027	Open
2024	April 15, 2025	April 15, 2028	Open
2025	April 15, 2026	April 15, 2029	Open

Two things that table does not show. First, a claim can be timely and still worth nothing: your refund is capped at what you actually paid in the three years before the claim, plus any filing extension. Filing on the last day of the window and expecting the full amount is how people get a letter instead of a check.

Second, a carryback runs on its own clock. The Form 1040-X instructions group the net Section 1256 contracts loss with the other carrybacks and give them all the same window: generally three years after the due date of the return, including extensions, for the year in which the loss arose. That is measured from the loss year rather than from the year being corrected, so it can reach back further than the ordinary rule does. Worth knowing that this comes from IRS guidance rather than the statute's own words: §6511(d)(2) sets the special period for "a net operating loss carryback or a capital loss carryback" without naming §1212(c) anywhere, though §6411(a) does describe a §1212(c) carryback in exactly those terms.

The common case: claiming a loss you never deducted

Here is the part that actually moves money for most people, and it has nothing to do with §1256.

A capital loss is not stuck in the year you lost it. Under §1211(b) a net capital loss offsets up to $3,000 of ordinary income per year ($1,500 if married filing separately), and whatever is left carries forward under §1212(b) with no expiration. It keeps offsetting income until it is used up.

The catch is that it only flows if it was claimed, and an unclaimed year is not merely paused. IRS Publication 550 says that when you figure the carryover to the next year you must take the current year's allowable deduction into account "whether or not you claimed it and whether or not you filed a return." So the $3,000 you could have used in a past year is spent from the carryover either way. Amending that year is how you get the benefit of it; skipping it does not push it forward to a better year.

Now the specific trap. If you treated a prior year as gambling, IRC §165(d) wagering losses come off only on Schedule A, and per IRS Topic No. 419 "you may deduct gambling losses only if you itemize your deductions." Most filers take the standard deduction. For them, gambling treatment deducted exactly zero of the loss, no matter how large it was. Capital treatment is different: the $3,000 under §1211(b) is not an itemized deduction and does not depend on itemizing at all.

That gap is the whole opportunity, and it is worth stating in dollars. Take a trader who lost $12,000 on Kalshi in 2023, had no capital gains, filed a normal return and deducted none of it. Illustratively, at a 22% marginal rate:

Year	Loss claimed	Approx. federal tax reduced	Carried forward
2023	$3,000 (amended)	~$660	$9,000
2024	$3,000 (amended)	~$660	$6,000
2025	$3,000 (amended)	~$660	$3,000
2026	$3,000 (original return)	~$660	$0

Roughly $1,980 recovered across three amended returns, with the last slice landing on a 2026 return that has not been filed yet. This is also why all three years get corrected rather than only the most recent one: each year's $3,000 comes out of the carryover whether it was claimed or not, so the only way to collect the 2023 slice is to amend 2023. Those figures are an illustration of the mechanism at a stated rate, not a calculation of anyone's liability, and there is a hard floor under all of it: an amendment refunds tax you actually paid. If you owed nothing in 2023, correcting 2023 refunds nothing, though it can still establish the carryforward into a year where you did.

Note what this is not. Nothing above is a carryback. The loss moves forward, needs no prior winning year, and does not depend on Section 1256 applying to event contracts. It only needs the trades to be capital rather than wagering, which is the reading we set out in are prediction markets taxed as gambling?.

What about the three-year carryback?

It exists, and one fact decides whether it is worth your time. Under §1212(c) an individual can elect to carry a net Section 1256 contracts loss back three years, but in each carryback year it offsets only net Section 1256 contract gains from that year, and it cannot create or increase a net operating loss. If you have no prior-year Section 1256 gains, which describes most people who came to Kalshi from sports betting and have lost since, the carryback recovers nothing. The election is made by checking Box D on Form 6781 for the loss year and entering the amount on line 6. If you filed that year without a Form 6781 at all, note that neither §1212(c) nor the form sets a deadline for the election, and both Publication 550 and the Form 1045 instructions contemplate making the carryback through an amended return; but silence is not permission, and whether a late election holds up is a question for your preparer rather than something to count on. The mechanics are in our Section 1256 60/40 guide.

Who this does not help

Being plain about this matters more here than anywhere else on the site, because an amendment is the thing we sell. Amending is not worth doing, or not possible at all, if:

• You paid no federal income tax in that year. A refund refunds tax you paid. No tax, no refund, though establishing a carryforward into a year you did pay can still be worth the filing.
• The year is closed. Past the §6511 window, a correct claim is still denied.
• You were counting on the carryback and have no prior Section 1256 gains. That is $0, not a smaller number.
• Your loss in each year was under $3,000. Below the §1211(b) cap, Section 1256 and ordinary capital treatment produce an identical result, so the aggressive position buys you nothing at all in that year.
• You are taking the §1256 route and cannot price your open positions at year end. That regime marks them to market on the last business day of the year, and a venue that published no price that day leaves you without a defensible number. Polymarket US has no pre-2026 year-end price history, so positions open across those dates fall in exactly that gap. Plain capital treatment does not have this problem, because it does not mark anything to market.
• You never filed for that year. That is an original return, not an amendment, and it is a different conversation with different deadlines.

What do you actually file?

One Form 1040-X per year, each filed separately, each carrying its own Part II explanation written in your own words. Attach the schedules that changed for that year, typically an amended Schedule D. If the filing is a carryback claim, the instructions say to write "Carryback Claim" at the top of page 1, and to attach an amended Form 6781 for each year the loss is carried to.

Amended returns can be e-filed for the current and two prior tax periods, which happens to be exactly the window still open for a refund; anything older goes on paper, as does an amendment to a prior-year return you originally filed on paper. Allow 8 to 12 weeks for processing, and up to 16 in some cases. Note that Where's My Amended Return does not track carryback applications, so that route gives you no status tool at all.

There is a faster route for carrybacks specifically, and it expires quickly:

	Form 1040-X	Form 1045	Do nothing
What it does	Corrects one prior year	Applies for a tentative refund from a carryback	The loss carries forward under §1212(b)
Deadline	3 years from filing, or 2 from payment	1 year after the end of the loss year	None
Speed	8 to 16 weeks	The IRS acts within 90 days	Recovered a year at a time
Scope	Any correction, including a carryback claim	Carrybacks and a few specific adjustments only	Nothing to file
How many	One per year amended	One, covering all three carryback years	None

Form 1045 is the faster instrument and the one with the shorter fuse: the instructions say to file it within one year after the end of the year in which the net Section 1256 contracts loss arose. Miss that and Form 1040-X is what is left, which is slower but runs on the much longer §6511 clock.

Two last things. Amending your federal return often means amending your state return as well, and states do not all follow the federal rules here; several decouple from the 60/40 split and from the carryback entirely. And a mistake on the first amendment is recoverable: you may file Form 1040-X for a year more than once, as long as each one is timely, though only three per year can be filed electronically.

How Realize helps

Realize does the bookkeeping, and nothing beyond it. We connect to your accounts read-only, pull the raw fills, and rebuild cost basis and year-end positions for each prior year, which is the thing an amendment cannot be built without: you can only claim what you can substantiate, and a year you cannot reconstruct is a year you cannot amend. We do not prepare your Form 1040-X, we do not sign it, and we do not tell you that a characterization is correct. That decision belongs to you and your tax professional.

For the wider picture, start at the Prediction Market Tax Center. The characterization this all turns on is in are prediction markets taxed as gambling?; the carryback mechanics are in the Section 1256 60/40 guide; the OBBBA 90% gambling-loss limit applies to tax years beginning after December 31, 2025, so it does not reach any of the years you would be amending today. If your records are the obstacle, see how to track prediction market trades for taxes, and you can price a year against all three treatments with our free prediction market tax calculator.

The bottom line

You can amend roughly three years back, one Form 1040-X per year, and the money usually comes from claiming a capital loss you never deducted: $3,000 against ordinary income per year under §1211(b), the rest carried forward under §1212(b), no prior winning year required. The Section 1256 carryback under §1212(c) is a different and much narrower thing, worth $0 to anyone without prior-year Section 1256 gains, and it rests on a characterization the IRS has never ruled on. Work out which of those you actually have, check the year is still open, and settle the position with a qualified tax professional before you file.

Status as of September 6, 2026. Filing deadlines and the characterization questions described here can move; verify the current position before relying on it.