How does the wash-sale rule apply if my spouse or my IRA buys the same stock?

The wash-sale rule disallows a loss if you buy a 'substantially identical' security within 30 days before or after the sale, and the IRS reads 'you' broadly. A purchase by your spouse counts, and so does a purchase inside your own IRA, including a Roth. The IRA case is especially harsh: the IRS has ruled the disallowed loss is permanently lost rather than added to the IRA's basis, so you get no future benefit at all. To harvest a loss safely, don't repurchase the same or a near-identical fund in any account you or your spouse control during the 61-day window. Buying a different fund that tracks a different index is the common workaround.