Roth conversion bracket-filling

See where thebracket fills up.

The gap years between retiring and the start of Required Minimum Distributions are often a household's lowest-tax window - earned income has stopped, RMDs have not yet forced large taxable withdrawals. Converting pre-tax money to Roth up to a bracket ceiling in those years can lower lifetime tax. Convert past the ceiling and the top of the conversion spills into the next bracket.

See the bracket math before December 31. Free, no brokerage login.

Open the Roth conversion calculatorModel a ladder in Ironlake →

The idea, with a number

What it means to fill the bracket.

Say a gap year leaves $40,000 of room before the next federal bracket begins. Converting roughly that $40,000 keeps the whole conversion at the lower bracket's rate. Convert $80,000 and the top half spills into the higher bracket. The discipline is to convert up to a ceiling you choose - and the case is strongest when your rate today is lower than the rate you (or your heirs) expect to pay later.

Where conversions go wrong

The four second-order effects to model.

  • The IRMAA two-year lookback. Medicare Part B and D premiums are surcharged on your income from two years prior. A large conversion at 63 can raise your premiums at 65 - a real cost that arrives late and is easy to forget.
  • Conversion-year vs. withdrawal-year state tax. If your current state taxes the conversion, you pay it now. Converting before a move to a lower- or no-tax state can be an expensive mistake; some states do not tax conversions at all.
  • The SECURE Act inherited-IRA rule. Most non-spouse heirs must empty an inherited IRA within 10 years. A pre-tax IRA left to a high-earning child can land entirely in their peak brackets - which often strengthens the case for converting in your own lower-bracket years.
  • Non-deductible basis. If part of your IRA is after-tax basis, only the pre-tax share of a conversion is taxable under the pro-rata rule. Modeling that keeps the conversion's real tax cost honest.

Ironlake's Roth Conversion Modeler runs a single year or a multi-year ladder with deterministic, year-by-year scenario math - quantifying the IRMAA two-year lookback, conversion-vs-withdrawal-year state tax, and non-deductible basis. It flags a non-spouse inherited IRA as non-convertible rather than modeling an heir's future 10-year drawdown. New to the mechanics? Read how Roth conversions work. Ironlake shows you the bracket math, the IRMAA exposure, and the multi-year trace; it does not tell you whether or how much to convert - that decision, ideally checked with your tax preparer, is yours.

Model a conversion