The backdoor Roth and the pro-rata rule

Earn above the Roth IRA income limits and the front door is closed. But there's no income limit on making a NONDEDUCTIBLE traditional IRA contribution, and no income limit on converting a traditional IRA to Roth. Contribute, then convert: the backdoor Roth. It's legal, explicitly acknowledged by Congress, and executed correctly it costs almost nothing in tax. Executed carelessly, the pro-rata rule turns it into a mess that follows you for years.

The clean version, step by step

1. Confirm you have NO pre-tax money in any traditional, SEP, or SIMPLE IRA (more on why below).
2. Contribute up to the annual limit ($7,000 in 2025; $8,000 if 50+) to a traditional IRA as a NONDEDUCTIBLE contribution. Leave it in cash or a money market fund.
3. Convert the entire balance to your Roth IRA — most brokerages do this online in minutes. Converting within days keeps taxable earnings near zero.
4. File Form 8606 with your tax return to report the nondeductible basis and the conversion. This form IS the paper trail — skip it and the IRS assumes the conversion is fully taxable.
5. Repeat every January. Invest the money once it's in the Roth.

The pro-rata rule: where it goes wrong

The IRS treats all your non-Roth IRAs as one pot. When you convert, you can't choose to convert 'just the after-tax dollars' — every conversion carries a proportional slice of pre-tax money across all traditional, SEP, and SIMPLE IRAs, measured on December 31 of the conversion year. A forgotten rollover IRA from an old job silently changes the math on your 'tax-free' backdoor.

Clearing the runway

• Roll pre-tax IRA balances INTO your current employer's 401k (if the plan accepts roll-ins — most large plans do). 401k balances don't count in the pro-rata calculation. This is the standard fix.
• Or convert the whole pre-tax balance to Roth and pay the tax — sensible only if the balance is small or you're in an unusually low-income year.
• Spouses are calculated separately: your rollover IRA doesn't contaminate your spouse's backdoor.
• The December 31 balance is what counts — clear the IRAs before year-end of the conversion year, not just before the conversion.

Is it worth the ritual?

$7,000/year into a Roth from age 35 to 60 at 7% growth is roughly $475,000 of tax-free money — versus the same investments in taxable costing tens of thousands in dividend and capital gains taxes along the way. Fifteen minutes a year plus one tax form is among the best-paid paperwork in personal finance. And it stacks with the mega backdoor (via your 401k) if your plan allows both.

The pro-rata math at different balances

Notice what the table implies: even a modest forgotten rollover IRA makes the conversion mostly taxable, and the leftover basis stays smeared across your IRAs — meaning Form 8606 arithmetic every year until the accounts are cleaned up. The fix is almost always worth doing first, not after.

A clean-runway walkthrough

Here's the sequence for someone starting dirty. In September, Maya asks her current 401k provider whether the plan accepts roll-ins of pre-tax IRA money (it does — most large plans do). In October she initiates a direct rollover of her $93,000 rollover IRA into the 401k; the check is made out to the plan, never to her, so nothing is taxable. By November her traditional IRA balance is $0. In early January she contributes $7,000 nondeductible to the empty traditional IRA, converts it to Roth three days later before it earns more than a few cents, and invests it inside the Roth. In April her preparer files Form 8606 showing $7,000 of basis in, $7,000 converted, $0 taxable. Total tax on the whole operation: effectively zero. The December 31 rule is why fall is the deadline that matters: the IRAs must be empty by year-end of the conversion year, and 401k roll-ins can take four to six weeks.

The annual ritual, compressed

1. 1
   Verify zero

   Confirm all traditional, SEP, and SIMPLE IRA balances are $0 (or will be by December 31). If not, roll them into a 401k before converting.

2. 2
   Contribute

   Deposit $7,000 ($8,000 if 50+) to the traditional IRA as a nondeductible contribution, left in cash or money market.

3. 3
   Convert within days

   Move the full balance to the Roth IRA online. Speed keeps taxable earnings at pennies.

4. 4
   Invest and document

   Buy your funds inside the Roth, then confirm at tax time that Form 8606 was filed and the 1099-R shows the conversion — not a taxable distribution.

Couples should run the ritual twice — each spouse with earned income (or a working partner, via spousal contribution rules) gets their own $7,000 of annual Roth space, doubling the long-run payoff for one extra set of clicks.

The bottom line

The backdoor Roth is a two-step dance with one fatal misstep: pre-tax IRA money sitting anywhere in your name on December 31. Sweep old IRAs into your 401k first, contribute nondeductibly, convert promptly, file Form 8606, repeat annually. Done right it's boring, cheap, and quietly worth six figures over a career — exactly the kind of boring that belongs in your calendar every January.