The bracket filling rules
By Mario Bailey · Published · Last reviewed
Seven constraints bound every bracket filling plan. Each one below states the rule, its source, and what the calculator does about it; the engine models all seven rather than footnoting them.
1. Conversions must complete by December 31
A conversion counts for the tax year in which it leaves the traditional IRA, not the year you file. There is no April catch-up: December 31 is the deadline (IRS Pub. 590-A). The calculator treats each projection year as a calendar-year conversion.
2. No undo since 2018
The Tax Cuts and Jobs Act repealed recharacterization of conversions (IRC section 408A(d)(6), effective 2018). Once converted, the tax is owed. This is why the calculator shows the bill per scenario before you act.
3. RMDs come out first
In any year a Required Minimum Distribution is due, the RMD must be withdrawn before any amount is converted, and the RMD itself can never be converted (IRS Pub. 590-B). The projection engine runs RMD as step 1 of every year for exactly this reason.
4. Your Required Beginning Date depends on your birth year
SECURE 2.0 set the RMD start age by cohort; the table below is computed from the same function the calculator uses. Conversions before this age face no ordering constraint.
| Birth year | RMDs begin at |
|---|---|
| Born before 1951 | Age 72 |
| Born 1951 to 1959 | Age 73 |
| Born 1960 or later | Age 75 |
5. Converted principal is locked for up to five years
Each conversion starts its own five-year clock (IRC section 408A(d)(3)(F)): withdrawing that principal within five taxable years triggers the 10% recapture penalty unless you are already 59.5. The lock ends at whichever comes first, clock expiry or age 59.5. The calculator flags any scenario that converts before age 54.5, because those conversions serve the full five-year lock; the clock runs out before age 59.5 can release it. The full mechanics, including the separate one-time clock on earnings, are at /learn/roth-conversion-five-year-rule/.
6. IRMAA looks back two years
Medicare premiums for a given year are set by your MAGI from two years earlier (SSA, 42 CFR 418.2135). A conversion at 63 raises premiums at 65. The calculator applies the two-year lookback from age 63 onward and flags tier crossings.
7. Conversions count against ACA subsidies before 65
Marketplace premium credits phase with MAGI, and crossing 400% of the federal poverty line can eliminate them (IRC section 36B). The calculator warns when a conversion year crosses the cliff while either spouse is under 65.
See which rules bind in your scenario
Sources: IRS Pub. 590-A and 590-B; IRC sections 408A(d)(6), 408A(d)(3)(F), 72(t), 36B; SSA / 42 CFR 418.2135; SECURE 2.0 Act of 2022 section 107.