She Did a Backdoor Roth. Her $300,000 Rollover IRA Made Almost All of It Taxable
A $300,000 pre-tax rollover IRA caused nearly all of a $7,500 backdoor Roth conversion to be taxable due to IRS pro-rata rules.
IRS Code Section 408(d)(2) aggregates all traditional, SEP, and SIMPLE IRAs on December 31, meaning a November rollover can retroactively ruin a January conversion.
Rolling pre-tax IRA balances into a 401(k), 403(b), or 457(b) before December 31 removes them from the pro-rata calculation, making backdoor conversions nearly tax-free.
The backdoor Roth is a two-step move for high earners who exceed direct Roth income limits: contribute to a traditional IRA on a non-deductible basis, then convert it to a Roth. The intuition is that money already taxed cannot be taxed again on conversion. For a saver with a clean IRA slate, that holds. For a saver carrying a large pre-tax rollover IRA from an old employer plan, it fails, and the failure is expensive.
A high earner contributes $7,500 on a non-deductible basis to a new traditional IRA and converts it a week later, expecting a tax-free conversion. She also holds a $300,000 rollover IRA from a prior 401(k), all pre-tax. On her return, almost the entire $7,500 conversion shows up as taxable income. The tax code does not let taxpayers choose which dollars to convert.
The governing provision is Internal Revenue Code Section 408(d)(2), which requires that all of a taxpayer's traditional, SEP, and SIMPLE IRAs be aggregated and treated as a single account for purposes of determining the taxable portion of any distribution or conversion. Any conversion carries the same proportion of pre-tax and after-tax money as the combined pool.
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A single year's non-deductible contribution of $7,500 alongside a $300,000 pre-tax balance represents a small fraction of the total, so nearly all of the converted amount is treated as pre-tax and taxed at ordinary rates. The pool is measured as of December 31 of the tax year, not the day of conversion. A rollover arriving in November can retroactively spoil a backdoor conversion completed in January.
The after-tax portion not treated as converted remains as basis spread across the IRA pool, recovered gradually over future distributions. The taxpayer has paid tax now and created a tracking obligation persisting for years. Basis is reported on Form 8606, which must be filed for every year a non-deductible contribution is made, even when no conversion happens. Skipping the form causes people to pay tax twice on the same dollars, first at conversion and again at withdrawal, because no record establishes that a portion was already taxed.
If the problem is pre-tax money in IRAs, the solution is to move that money somewhere the pro-rata calculation cannot see it. Employer retirement plans, including 401(k), 403(b), and governmental 457(b) plans, are excluded from the IRA aggregation pool. Rolling the $300,000 pre-tax IRA balance into a current employer plan that accepts incoming rollovers leaves only the after-tax contribution in the IRA, so a subsequent conversion is nearly or entirely tax-free.
Three conditions matter, starting with the employer plan accepting incoming rollovers. The rollover must be completed before December 31. Employer plans also offer narrower investment menus and less flexibility than an IRA. Self-employed savers can achieve the same result by opening a solo 401(k) that accepts rollovers and moving the pre-tax IRA balance there.
Someone with a large pre-tax IRA, no access to a plan accepting incoming rollovers, and no intention of moving the money should generally not attempt a backdoor Roth. The tax cost swamps the benefit. A spouse's balances are counted separately, so one spouse's rollover IRA does not contaminate the other's contribution.
Each Roth conversion carries its own five-year holding period for penalty-free withdrawal of the converted amount before age 59½, separate from the five-year rule for Roth earnings. The IRS has publicly indicated it will not challenge back-to-back contribution and conversion under the step transaction doctrine, and practitioners routinely execute them within days.
The 2026 traditional IRA contribution limit is $7,500, with an additional $1,100 catch-up for savers age 50 and older. Before attempting a backdoor Roth, answer this question: What will the total balance of every traditional, SEP, and SIMPLE IRA in your name be on December 31? If that number is large and cannot be moved into an employer plan by year-end, the strategy is not what it was sold as.
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