The rule is older than most of the funds it catches. Section 1091 disallows a loss if you buy a substantially identical security within 30 days either side of the sale. That is 61 days in total, counting the day of the sale itself.
Inside an ordinary taxable account this is a delay rather than a penalty. The disallowed loss is added to the cost of the replacement shares and the holding period carries over. You get the deduction back whenever you finally sell.
The IRA version has no such mechanism. Revenue Ruling 2008-5 applies the wash sale rule when the repurchase lands in your own IRA. The ruling does not let you raise the basis of an IRA. The loss is disallowed with nothing to attach it to.
So the same mistake carries two different prices. Made inside a taxable account it costs you timing. Made once across the line into an IRA it costs you the loss outright, and there is no filing that reverses it.
Then there is the part the paperwork hides. A broker reports wash sales for identical securities held in one account. A second account at the same firm, a spouse’s account, another broker, your own IRA: none of that is visible to it. The form is not the referee, and the duty to report sits with you.
Which is why December trades deserve a list. Your own list, written before the sale rather than after it. It covers every account in the household, not only the one you are selling from.
Before you sell anything at a loss this year, write down every account that could hold the same security. Taxable, IRA, Roth, a spouse’s accounts, a second broker, and any automatic dividend reinvestment. Reinvestment is the quiet one, because it buys without asking you first.