The $184K mistake IRA savers could make

Paper or plastic? Mac or PC? Roth IRA or traditional IRA? The first two are largely matters of personal preference; the third strictly of taxes — or so you have probably been told.

But a new NerdWallet analysis reveals that savers who make the maximum IRA contribution each year will always net more after-tax retirement dollars with a Roth IRA than they will with a traditional IRA, regardless of their current and future tax rates.

The Roth advantage is not trivial: In several tax scenarios, the after-tax value of the Roth stands six figures ahead of the value of the traditional IRA. One scenario shows a $184,364 Roth IRA advantage.

The general advice on IRAs goes this way: If your tax rate is lower now than you expect it to be in retirement, a Roth IRA — which offers no immediate tax deduction, but allows tax-free distributions in retirement — is the right choice for you, provided you don't exceed the income limits for a Roth.

If you expect your tax rate to drop in retirement, standard advice says to go with a traditional IRA, which offers a tax deduction on contributions now in exchange for taxed distributions later.

The NerdWallet analysis shows that, for savers who make the maximum IRA contribution each year ($5,500, or $6,500 if you're 50 or older), the Roth will always yield more after-tax value than a traditional IRA.

Why does the Roth win? It relates to the value of a dollar in a Roth IRA compared to the value of a dollar in a traditional IRA.

With a traditional IRA, your money is going in pretax, which means your cost is only the amount of the contribution. That makes it seem like the traditional IRA is a better deal, and in the short run, it is.

But when looking at the value of each account at retirement, you have to compare the Roth IRA balance to the after-tax balance of the traditional IRA.

When you pull $30,000 out of a traditional IRA in retirement, the IRS gets a little piece of that pie — how little depends on your future tax rate, but several thousand dollars, to be sure. When you pull that $30,000 out of a Roth IRA, you're putting $30,000 into your pocket free and clear.

To account for that tax burden in retirement, a traditional IRA needs a larger balance to equal the value of a Roth IRA. And since the contribution limit on these accounts is the same — that $5,500 is a combined limit between the two — the only way to build that larger balance is to supplement it by also contributing to a separate investment account.

To do that, you would need to take the tax savings netted by the traditional IRA contribution each year and put it in a brokerage account, choosing investments that mirror what's in your IRA. At a 25 percent current effective tax rate and the maximum $5,500 contribution, that would mean investing $1,375 in tax savings from that tax deduction.

If, on the other hand, you take that tax savings and absorb it into your budget — either because it simply reduces your tax bill come filing time, so you never actually get your hands on it, or because you didn't know the importance of investing it — you would end up short of what you could have accumulated in a Roth IRA, no matter what your tax bracket.

Again, the figures in the analysis assume the saver is making maximum annual contributions. Savers who make less than the maximum contribution each year may find traditional IRAs more competitive for their tax scenario — or they may not.

Another possible Roth upside: Roth IRA rules don't require minimum distributions — mandatory withdrawals set forth by the IRS — but a traditional IRA owner must begin withdrawals at age 70½.

That's worth weighing if you want to pass money on to heirs.

If you are committed to making annual contributions to your IRA, the choice between a Roth or traditional IRA requires an analysis of your own saving habits.

Some very disciplined savers will be able to do that. But for the many others, the Roth IRA is the better choice.