Pre-Tax or Roth 401k: What The Math Actually Says
Written by Chris DeVito
A question as old as time itself. Should I pay taxes now (Pre-Tax 401k) or later (Roth)? The honest answer depends entirely on how you frame the comparison, and most people are framing it wrong.
It's one of the most common questions I get from Big Law attorneys. Most people expect a simple answer. The reality is the math depends heavily on how you set up the comparison.
The standard version of this debate, invest a smaller after-tax amount in a Roth vs. the full pre-tax amount in a traditional 401(k), is actually flawed. It compares different amounts of invested capital. The real question is: if you're going to put $24,500 into your 401(k) either way, which structure puts more money in your pocket?
This example is hypothetical and for illustrative purposes only. It is based on assumed rates of return, tax rates, and time horizons that may not reflect actual market conditions or individual circumstances. Actual results will vary.
Let’s take a look assuming:
- Age - 40
- Income - $500,000/year
- Location -New York City
- 401(k) contribution -$24,500 (2026 max, under 50)
- Contribution frequency -One-time, never touched
- Growth rate (accumulation) -10% average annual
- Accumulation period -25 years (age 40 → 65)
- Withdrawal strategy - 4% annual draw, 7% growth
- Retirement window - 25 years (age 65 → 90)
Step 1: The NYC Tax Reality
At $500,000 in New York City, you're stacking three layers of tax on every dollar. This is the rate that matters for this decision:
Federal Marginal Rate -37%
NY State Top Rate -10.9%
Combined Marginal Rate ~51.8%
Fed + NY State + NYC local (3.88%)
That combined rate is the foundation of this entire analysis. It's what you save by going pre-tax and it's what determines how expensive Roth really is.
Step 2: The True Cost of Each Option
Here's where most comparisons go wrong. They assume the Roth investor puts in a smaller after-tax amount. But let's say you're committed to maxing out at $24,500 regardless. The real difference is what it costs you to get that money into the account.
The pre-tax 401(k) saves you $12,685 today. The Roth requires you to earn an extra $26,305 just to fund the same contribution.
At a 51.8% marginal rate, to put $24,500 into a Roth after taxes, you'd need to earn roughly $50,805 gross, meaning $26,305 goes to taxes before a single dollar hits your account. The pre-tax route skips that bill entirely and saves you $12,685 on your current return.
Pre-Tax: Tax Impact This Year – Saves you $12,685
Taxes saved on the $24,500 contribution at 51.8% marginal rate
Roth: Tax Cost This Year – Costs you $26,305
Gross income needed to net $24,500 after-tax: roughly $50,805
Both accounts receive the same $24,500. Both grow identically. The first meaningful difference is purely in the upfront tax treatment.
Step Three: 25 Years of Growth
Left untouched from age 40 to 65, growing at 10% per year, both accounts reach the same balance:
Both Accounts at Age 65
$265,450
Compounding does the same work regardless of tax structure
Step Four: The Retirement Tax Bill
Using a 4% annual draw while the remaining balance continues growing at 7%, the account sustains itself through retirement and actually grows. At a 30% effective tax rate in retirement (federal + state, on a meaningfully lower income than peak earning years), here's how the pre-tax account plays out over 25 years:
Starting Annual Withdrawal (Age 65)
- $10,618 which is 4% of $265,450
- Total Withdrawn Over 25 Years is $373,203
Balance grows as withdrawals are taken
On those $373,203 in withdrawals, the pre-tax account owes taxes at an estimated 30% effective rate in retirement, a significant drop from the 51.8% marginal rate during peak earning years.
Total Taxes Paid in Retirement (Pre-Tax)
$111,961
30% effective rate on $373,203 total withdrawals
In some cases, a pre-tax strategy may produce more favorable results, particularly if:
- retirement tax rates are significantly lower,
- tax savings are reinvested effectively,
- or current cash flow constraints favor upfront tax deferral.
Total Taxes Paid in Retirement (Roth)
$0 since ALL withdrawals are tax-free
The Full Comparison
Now we can see the complete picture side by side, same $24,500 contribution, same growth, different tax treatment at each end.
| Pre-Tax 401(k) | Roth 401(k) |
Amount contributed | $24,500 | $24,500 |
Tax impact at contribution | −$12,685 saved | +$26,305 paid |
Value at age 65 | $265,450 | $265,450 |
Total withdrawn (age 65–90) | $373,203 | $373,203 |
Taxes paid in retirement | $111,961 | $0 |
Net spendable from withdrawals | $261,242 | $373,203 +$111,961 |
Remaining balance at 90 | $519,000 | $519,000 |
On an apples-to-apples basis, same dollars invested, the Roth produces $111,961 more in net spendable retirement income. That gap is exactly equal to the deferred tax bill on the pre-tax account. Which makes sense: the Roth simply eliminates that liability entirely by paying it upfront at a lower gross cost.
Under the assumptions used in this example, the Roth structure results in higher net after-tax withdrawals; however, outcomes will vary significantly based on individual tax rates and time horizon.
There are still a lot of variables and some that cannot be fully answered. The main things to consider when choosing for yourself are…
- Will you invest the difference that pre-tax saves you?
- How long do you have until accessing the funds?
- How much of your retirement is already pre-tax (think RMDs in the future)
- Are you likely to have a significant reduction in spending?
- This scenario dropped the effective tax rate by 40%, is that realistic for you?
IMPORTANT DISCLOSURES
This material is provided for informational and educational purposes only and should not be construed as investment, tax, or legal advice.
This example is hypothetical and for illustrative purposes only. It is based on assumptions regarding rates of return, tax rates, and time horizons that may not reflect actual market conditions or your individual circumstances. Actual results will vary.
The analysis assumes consistent rates of return and that any tax savings from pre-tax contributions are not separately invested. Changes to these assumptions may materially impact the results.
Tax laws and rates are subject to change and will vary based on individual circumstances. Investors should consult with a qualified tax professional before making any decisions regarding tax-advantaged accounts.
Investing involves risk, including possible loss of principal. Past performance and hypothetical illustrations are not indicative of future results.
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