1099-B Box 1g: Reading the Wash Sale Loss Disallowed
A figure in box 1g means part of a loss was moved into the basis of the shares you bought back, where you can follow it to a later sale.
Short answer
Box 1g shows the part of a loss your broker disallowed because you also bought that security during a window of 30 days before or after the sale. The loss is not gone: it is added to the cost basis of the shares you bought back, and on Form 8949 it is reported with code W.
You sold at a loss, opened your 1099-B, and found a number in box 1g. That number is the wash sale loss disallowed: the part of the loss your broker held back because you repurchased the same security inside the window that runs 30 days either side of the sale. The IRS 1099-B instructions and Publication 550 set out what happens next. The disallowed amount is folded into the replacement lot’s basis, and the time you held the sold shares counts toward the replacement lot’s holding period too.
So the loss is deferred. You get it back on the day you sell the replacement lot and stay out.
For the rest of the form, line by line, see how to read Form 1099-B. This page stays on box 1g.
What sets the number
Your broker runs a fixed test. Did you sell at a loss? Did you buy the same security in the same account within the 61-day window, which is 30 days before the sale, the sale day itself, and 30 days after? If both answers are yes, the matching part of the loss lands in 1g.
Gains never trigger it. A sale at a profit leaves 1g empty no matter how fast you bought back in.
Brokers match on identical securities, meaning the same CUSIP, and only inside the one account. That narrow test explains most of the surprises. The tax rule itself reaches further, to substantially identical securities and to purchases made in any account you or your spouse control, so a broker can report 1g correctly by its own test and still leave you with a wash sale it never saw.
A full wash sale, worked through
Every figure below is hypothetical.
Say you bought 100 shares at 50.00 and sold them at 44.00. Within 30 days you bought 100 shares back at 45.00. Some weeks later you sold those replacement shares at 48.00 and did not buy again.
The cash check is the useful part. Across both trades you lost 300.00, and once the 600.00 moves into the replacement basis, the tax figures add up to the same 300.00. Without the adjustment the later sale would show a 300.00 gain, and you would be taxed on a profit you never made.
The holding period carries over too. The time you held the shares you sold is added to the replacement shares, which can decide whether the later sale is short or long term.
When you buy back fewer shares
The disallowed part follows the share count. Sell 100 shares at that same 600.00 loss and buy back only 40, and only 40% of the loss is held back.
The 240.00 rides in those 40 shares until you sell them.
Why 1g can look wrong
Most of the time it isn’t wrong. It is answering a narrower question than the one you have in mind.
A year-end sale is the usual case. You sell at a loss in late December, the 30 days after the sale run into January, and you buy back on the second business day of the new year. The loss sits on this year’s 1099-B, so this year’s box 1g shows the disallowance, even though the purchase that caused it belongs to next year’s statement.
Multiple lots are the other. When you bought a position in pieces and sold only some of it, or bought back in several small orders, the broker has to match particular replacement shares to particular loss shares, and the result can spread one disallowance across several lines or carry part of it forward again if a replacement lot is itself sold at a loss and bought back inside the window. Each line can be correct and the total still look strange.
Check both before you call the broker.
What box 1g leaves to you
The first gap is purchases outside the account. A buy of the same stock in your second brokerage account, in your spouse’s account, or in an IRA never reaches 1g, and the IRA case is the harsh one: under Rev. Rul. 2008-5, buying in your IRA within the window disallows the loss permanently, with no basis increase anywhere to recover it later.
Lookalike securities are the second. A purchase that is substantially identical without sharing the CUSIP stays outside the broker’s test.
To check these, take the date of each losing sale, run it through the wash sale window calculator for the 30 days before and after, and scan every account you and your spouse hold for buys inside that range.
Getting 1g onto your return
On Form 8949, the disallowed amount goes in column (g), and code W goes in column (f). That is true for amounts your broker put in 1g and for any you found yourself. Column (h) then works out as proceeds minus basis plus the adjustment, so the full replacement above comes to 4,400.00 minus 5,000.00 plus 600.00, which is zero. The full mechanics of the wash sale rule are in the wash sale entry. If you found an outside-account wash sale, or if the 1g figures and your log disagree after checking lots and year-end dates, take both to a tax professional before you file.
Also asked
- Where does a box 1g amount turn up again later?
- In box 1e of the line where you eventually sell the replacement shares. Their basis already includes the disallowed loss, so that later sale shows a smaller gain or a bigger loss than the raw prices suggest.
- Can box 1g ever be larger than the loss on its line?
- It should not be. Box 1g holds the disallowed part of that sale's loss, so it runs from zero up to the full loss. A figure above the loss is worth raising with your broker.
- Can I report a wash sale my broker never put in box 1g?
- Yes, and you are expected to. The adjustment goes on Form 8949 in column (g) with code W, the same as one your broker reported. Ask a tax professional to check the figure before you file.