How to Amend a Tax Return for Prediction Market Losses

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 October 2026 looks like this:

Filed your 2022 return on extension? The three years run from the date you filed it, so a return filed on October 16, 2023 can be amended until October 16, 2026.

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 can move 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:

Roughly $1,980 potentially recovered across three amended returns, with the last slice landing on a 2026 return that has not been filed yet. In this example each year's $3,000 comes out of the carryover whether it was claimed or not, so the 2023 slice is only collected by amending 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 paid no federal tax for 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, the question covered 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, 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; neither addresses a late election directly, so whether one holds is unsettled. The mechanics are in our Section 1256 60/40 guide.

What the two moves each rest on

Section 1256 is not an election. If it applies to an instrument it applies, and if it does not, checking a box cannot make it. So correcting the character of a prior year is a correction, not a position opted into, and the same is true of claiming a capital loss that was allowable and not taken.

Filing a Form 1040-X is still an affirmative claim, made on a question with no IRS guidance and no court decision behind it, and the two moves on this page rest on different things. The $3,000 offset and the carryforward need the trades to be capital rather than wagering; none of that depends on Section 1256 applying. The carryback depends on Section 1256 applying to event contracts.

Who this does not help

Being plain about this matters more here than anywhere else on the site, because carryback estimates are part of what we build. 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.
• You are amending only to switch to Section 1256, and 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 Section 1256 adds nothing 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 usable number. Polymarket US's first year end with published prices is December 31, 2025, so earlier year ends have none. 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 Form 8949 and 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 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. For a 2025 loss, that is December 31, 2026. 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 Kalshi and Polymarket US 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. Plans and prices are on the pricing page.

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. Which of those applies to a given history, and whether the year is still open, decides what amending recovers.

Status as of October 15, 2026. Filing deadlines and the characterization questions described here can move.

Questions people ask

Can I amend a prior-year tax return to claim Kalshi or Polymarket losses?

+−

Yes, if the year is still open. You file Form 1040-X for that year, and you generally have three years from the date you filed the original return, or two years from the date you paid the tax, whichever is later. An amendment only produces a refund to the extent you actually paid federal income tax for that year. How prediction-market contracts are characterized is unsettled; the IRS has issued no guidance on it.

How far back can I amend my tax return?

+−

Under IRC §6511(a) the window is three years from the date you filed the return or two years from the date you paid the tax, whichever is later. A return filed before its due date counts as filed on the due date, so an early filer gets the same deadline as an April filer. There is also a separate cap: your refund is limited to what you actually paid in the three years before you file the claim.

Can I carry back my prediction-market losses to a prior year?

+−

Only against prior-year Section 1256 gains. IRC §1212(c) lets an individual elect to carry a net Section 1256 contracts loss back three years, but in each carryback year it can offset 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, the carryback recovers nothing. It is also contingent on Section 1256 applying to event contracts, which is unsettled.

Do I need a prior winning year to get a refund from amending?

+−

Not for the common case. Claiming a loss you never deducted works forward, not backward: under §1211(b) a net capital loss offsets up to $3,000 of ordinary income per year ($1,500 if married filing separately), and the remainder carries forward under §1212(b) with no expiration. That needs no prior gains at all. A prior winning year is only required for the §1212(c) three-year carryback.

Can I combine three years of losses onto one amended return?

+−

No. A return covers one tax year, and the IRS instructions say to file a separate Form 1040-X for each year you are amending. A loss belongs to the year you incurred it. What moves between years is the unused portion of a capital loss, which carries forward under §1212(b) and has to be claimed on each later year in turn.