Usually in the years between retiring and the start of required minimum distributions, when your income is temporarily low and the lower brackets sit empty. Convert in December once the year is known, fill a bracket without overflowing it, and…

Pay in at least 90% of your 2026 tax, or 100% of the tax shown on your 2025 return — 110% if your 2025 adjusted gross income was over $150,000 — and the underpayment penalty cannot be charged, however large…