Roth Conversion Basics: Mechanics, the Five-Year Rule, and the Real Tradeoffs

A Roth conversion is a taxable transfer of money from a pretax retirement account (traditional IRA, 401(k) rollover IRA, certain SEP/SIMPLE accounts) to a Roth IRA. The converted amount is added to your taxable income for the year of conversion and taxed at your marginal rate. In exchange, the money grows tax-free going forward, and qualified withdrawals are tax-free.

There is no income limit on Roth conversions, unlike direct Roth contributions (which phase out at higher incomes). There is also no dollar limit on conversions — you can convert as much or as little as you want in a given year, which is the core of the strategic flexibility.

The "five-year rule" for Roth IRAs is two separate rules that often get conflated.

The first rule applies to earnings. Earnings in a Roth IRA are only qualified (tax-free and penalty-free) if the Roth IRA has been open for at least five tax years and the owner is over 59½ (or meets another qualifying condition like death or disability). This rule is satisfied once per person — the clock starts with the first Roth IRA contribution or conversion and applies to all future Roth IRAs.

The second rule applies specifically to conversions. Each conversion has its own five-year clock before the converted principal can be withdrawn without the 10% early-withdrawal penalty, if the owner is under 59½. For owners over 59½, this rule is generally moot. For early retirees considering the Roth conversion ladder strategy, the per-conversion five-year clock is the binding constraint.

The core strategic question for a Roth conversion is: is your marginal tax rate today lower than your expected marginal tax rate at the time the money would otherwise be withdrawn? If yes, converting is positive-expected-value. If no, it is not.

The "low-tax window" for many pre-retirees is the years between retirement and either Social Security claiming or Required Minimum Distributions (RMDs at age 73 under current law). In this window, wage income has stopped, Social Security has not started, and RMDs have not begun — producing a temporarily low-income window where conversions fill up the lower brackets at bargain rates.

Conversions tend to underperform when: current-year marginal rate is already high (still working, peak earning years); the user plans to leave the pretax money to charity (which receives it tax-free anyway); or the conversion pushes the user into an IRMAA tier two years later.

The converted amount is included in MAGI for the year of conversion, which determines IRMAA (Medicare premium surcharge) two years later for anyone Medicare-eligible. A conversion at age 63 affects the Medicare premium at age 65. A conversion at age 65 affects the Medicare premium at age 67.

This interaction matters because IRMAA tiers are cliffs — a conversion that pushes MAGI one dollar over a tier boundary triggers the full surcharge of the next tier, which can be several hundred dollars per month per spouse. Thoughtful planning models the IRMAA surcharge as a real marginal cost when sizing the conversion, not as a separate footnote.