What it means
Retirement saving comes in two flavours, and the difference is simply when the tax is paid. A pre-tax contribution reduces taxable income now and is taxed in full on withdrawal, while an after-tax contribution gives no deduction now and is largely untaxed later.
The permanent record created by an after-tax contribution is called the basis. Keeping accurate records of that basis is essential, because without it a saver can end up paying tax a second time on money that was already taxed on the way in.
There are two distinct versions worth separating. Roth-style contributions are made after tax and, if the holding conditions are met, both the contributions and the growth come out tax free, whereas plain after-tax contributions to a traditional plan return the basis tax free but tax the growth as income.
The reason to choose after-tax is mostly a bet on future tax rates. If you expect to face a higher rate in retirement than you do today, paying tax now at the lower rate leaves you better off, and the reverse holds if you expect your rate to fall.
There is a second, less obvious attraction. After-tax contributions often sit outside the normal deferral limits, which lets high earners put substantially more into a plan than the standard cap allows once employer contributions are counted.
In practice
Real-world examples.
Example
A sales director already contributing the standard deferral maximum adds $22,000 of after-tax contributions to her workplace plan. She keeps the annual statement showing the basis so that the money is not taxed again when she draws it.
Example
A graduate joiner on a modest salary chooses Roth-style after-tax contributions on the reasoning that his marginal rate today is low and is likely to be higher for most of his career. He accepts a smaller pay packet now for tax-free withdrawals later.
Example
A finance manager reviewing an acquired company's payroll finds after-tax contributions coded as pre-tax for three years. The correction requires amended filings and a rebuild of each employee's basis records before anyone retires.
Formula
Calculation
Basis = total after-tax contributions made
Taxable portion of a withdrawal = withdrawal amount - proportionate share of basis
Net take-home cost of a pre-tax contribution = contribution x (1 - marginal tax rate)
Worked example. Priya earns $120,000 and contributes 8% of salary, or $120,000 x 0.08 = $9,600, on an after-tax basis. Her marginal rate is 24%.
Because there is no deduction, the full $9,600 comes out of taxed income and her take-home pay falls by $9,600. The same $9,600 contributed pre-tax would have reduced her take-home pay by only $9,600 x (1 - 0.24) = $7,296, a difference of $9,600 - $7,296 = $2,304 in the current year.
Years later the account attributable to those contributions is worth $24,000.
Basis = $9,600
Growth = $24,000 - $9,600 = $14,400
If the plan is a traditional one holding plain after-tax money, the basis returns tax free and only the growth is taxed. At a retirement marginal rate of 22%, tax on withdrawal = $14,400 x 0.22 = $3,168, leaving $24,000 - $3,168 = $20,832. Had the whole $24,000 been pre-tax money, tax at 22% would be $24,000 x 0.22 = $5,280, leaving $18,720, so the after-tax route delivers $20,832 - $18,720 = $2,112 more at withdrawal in exchange for the $2,304 of tax paid up front.Case study
Seen in the real world.
Wexley Dental Group is an illustrative, fictional practice with 40 staff whose four partners had each been contributing the standard pre-tax maximum and little else. Their adviser pointed out that the plan allowed additional after-tax contributions well above that cap.
One partner earning $310,000 began contributing an extra $28,000 a year on an after-tax basis. Because no deduction was available, his take-home pay fell by the full $28,000, roughly $9,000 more than an equivalent pre-tax contribution would have cost him at his 32% marginal rate. Over eight years he contributed $224,000 of basis, and the account attributable to it grew to $362,000.
When he began drawing on it, the $224,000 of basis came back untaxed and only the $138,000 of growth was taxable. In this fictional example the practice also changed its payroll process so that after-tax contributions were tracked in a separate ledger from the first day, because the adviser's main warning had been that lost basis records, not poor investment returns, are what usually destroy the benefit.
Watch out
Common mistakes.
- Failing to keep basis records. Without documented proof of after-tax contributions, the same money can be taxed a second time on withdrawal.
- Assuming all after-tax contributions are Roth contributions. Roth money can come out entirely tax free if conditions are met, while plain after-tax money in a traditional plan still has its growth taxed.
- Comparing pre-tax and after-tax contributions by the amount paid in. The correct comparison is the effect on take-home pay now against the tax due on withdrawal later.
Questions
People also ask.
When does an after-tax contribution make sense?
Mainly when you expect a higher tax rate in retirement than today, or when you have already reached the pre-tax deferral limit and want to save more.
Is the growth on after-tax money always tax free?
No, only in Roth-style arrangements meeting the holding conditions; in a traditional plan the growth is generally taxed as income on withdrawal.
Do employer contributions count as after-tax?
Normally no, employer contributions are usually pre-tax, so they create no basis and are fully taxable when drawn.
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