The Backdoor Roth: Who Actually Needs One

Somebody asked me about backdoor Roths at a birthday party, which is how I know the phrase has fully escaped into the wild. He was 31 and earned $74,000.

He did not need one.

He could contribute to a Roth IRA directly, from his phone, in about four minutes. The backdoor is a workaround for a door that was not locked for him.

That is the most useful thing I can tell most readers, so it goes first rather than at the end.

Who it is genuinely for

There is an income band above which you cannot contribute to a Roth IRA directly at all. If your MAGI, modified adjusted gross income, sits below the bottom of that band, contribute to a Roth the ordinary way and stop reading about backdoors.

If your MAGI sits above the top of it, you have three options: skip the Roth, use a Roth 401k at work if your plan offers one, or take the two step route below.

The two steps

Step one, contribute to a traditional IRA and do not deduct it. Anybody with earned income can do this at any income level, because the traditional contribution itself has no income ceiling. Only the deduction does.

Step two, convert that traditional IRA to a Roth IRA. There has been no income limit on Roth conversions since 2010.

The money went in after tax, so if it has not grown between the two steps there is little or nothing to tax on the way across. That is the whole trick, and described that plainly it sounds too easy.

The rule that ruins it

The pro-rata rule. When you convert, the IRS treats every traditional, SEP and SIMPLE IRA in your name as a single pot, and you cannot choose which dollars move. Whatever proportion of the pot is after tax money is the proportion of your conversion that comes across tax free.

Say you have a $63,000 rollover IRA from an old job, all of it pre-tax, and you add $7,000 of after tax money. The pot is $70,000 and $7,000 of it is after tax, which is 10 per cent, because 7,000 divided by 70,000 is 0.10.

Convert $7,000 and only $700 comes across tax free. The other $6,300 is taxable income. On a 24 per cent marginal bracket that is $1,512 in tax, because 6,300 times 0.24 is 1,512, on a move somebody told you was free.

And the $63,000 does not vanish. Your after tax basis is now spread across the whole pot and you will be untangling it on every future conversion, which is a chore that outlives the original mistake by years.

One timing detail that saves people: the balance counted is the combined value on December 31 of the conversion year, not the day you converted. Clearing the pre-tax IRA in November of the same year still works. Clearing it in January of the next year does not.

How people clear the pot

Roll the pre-tax IRA into your current employer's 401k. Workplace plan balances are not counted in the pro-rata calculation, so moving the money there empties the pot without triggering any tax.

Not every plan accepts incoming rollovers. Ask your plan administrator whether the plan permits roll-ins before you contribute a dollar, not after, because the order matters and December arrives faster than you think.

The other route is converting the entire pre-tax balance to Roth and paying the tax on all of it this year. On $63,000 at a 24 per cent marginal rate that is around $15,120 of tax, though converting that much usually pushes part of it into a higher bracket, so the real figure is worse than the simple multiplication.

The paperwork you cannot skip

Form 8606 is how you tell the IRS the contribution was made with after tax money. Skip it and there is no record of your basis, which means you can end up paying income tax a second time on money you already paid tax on.

The forms also arrive out of order, which confuses everybody in year one. The conversion shows up on a 1099-R in January, and the contribution shows up on a 5498 in May, months after you have filed.

File the 8606 every year you do this. It is one page and it is the only proof you have.

The other manoeuvre with a confusingly similar name

A mega backdoor Roth is a different thing that happens inside a 401k rather than an IRA, and the similar name causes a lot of crossed wires.

It only works if your plan permits after tax contributions above the normal employee limit and also permits either in-plan Roth conversions or in-service withdrawals. Plenty of plans permit neither, so the first move is asking your plan administrator those two specific questions rather than reading about it.

Where a plan does allow it, the sums involved are far larger than the IRA version, and the pro-rata rule above does not touch it, because no IRA is part of the transaction.

The honest verdict

Three conditions have to be true. Your income is above the Roth band, you have no pre-tax IRA balance or you can clear it before December 31, and you are willing to file one extra form every year.

Miss the first and it is unnecessary. Miss the second and it is expensive. Miss the third and it becomes a mess your future self has to reconstruct from statements.

This is also a step Congress has proposed closing more than once. It is legal as of 2026, and anybody planning around it for the next twenty years should assume it might not survive all of them.

Log in to every retirement account in your own name rather than your employer's, and write down next to each one whether the money in it is pre-tax or after tax. If the pre-tax column totals zero, the door is open. If it does not, your first move is a call to your 401k provider asking two words: roll ins.