A surviving spouse inheriting a large pre-tax 401(k) faces a "widow's penalty" as tax brackets narrow significantly when filing singly, doubling marginal tax rates on the same income. Social Security benefits become more taxable, and higher income can trigger costly Medicare surcharges. Strategies to mitigate this include Roth conversions while both spouses file jointly, draining the older spouse's 401(k) first, and purchasing life insurance to cover future tax costs. The final joint return year is the last chance for large conversions at lower rates.