Before the next deposit: check eligibility and remaining Roth room, then check when the money is needed and the tax path. The comparison applies only after the reserve, employer-plan and debt decisions.
Opening a Roth IRA is not the same as using it. This comparison asks whether the next eligible long-term deposit belongs in a Roth IRA or a taxable brokerage account.
Under the model below, the Roth path finishes $31,535 ahead on the year-30 statement and $73,520 ahead in spendable value after an assumed full sale. The IRA modeled here is a Roth IRA. A near-term cash need, a 0 percent rate on the modeled qualified dividends and gains, or unavailable direct Roth room can change the order.
Theo opened a Roth IRA in February 2026. In the hypothetical Roth-funded path, the opening $3,000 is assigned to tax year 2025 and the first year-end $6,000 to tax year 2026; each later deposit belongs to its own tax year. In the taxable-only path, he sends the opening $3,000 and every later deposit to brokerage instead. The Roth exists but remains empty.
Both paths hold the same index fund and receive the same deposits. One routes every dollar to the Roth IRA; the other routes every dollar to taxable. Theo is 40 when the model opens and 70 at the year-30 comparison, so more than five tax years have elapsed and the modeled Roth distribution is qualified. He is a hypothetical composite, not a real person.
The comparison is federal only, for a single filer. It leaves out state tax, the net investment income tax, fund fees, trading costs and capital-gain distributions, and it does not rank a Roth IRA against emergency cash, an employer match or debt repayment. Those decisions come first and sit outside this arithmetic.
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The Roth he opened but never funded
The practical choice is the deposit destination, repeated once a year for thirty years.
An empty account uses no contribution capacity. Money has to go in, and it has to go in for that tax year. Nothing else counts.
The case for filling the brokerage account first is real. No contribution limit. No income phase-out. No age rule on withdrawals. That flexibility can matter for a dated goal, although the investment inside the account still has to match the time horizon.
But Theo’s money had no job for thirty years. The flexibility never helped him, while the annual tax drag kept reducing what went back to work.
ICIβs household survey supplies context for account use. Among households owning a traditional or Roth IRA in mid-2025, 62 percent made no contribution for tax year 2024. That number does not prove those households made a mistake. ICI counts households rather than people and reports several legitimate reasons for noncontribution. It does show that owning the account and using the annual room are separate acts.
Funding a Roth does not lock every dollar away until 59½, either. IRS ordering rules treat regular contributions as distributed first; conversions and earnings follow separate rules.
This is the same arithmetic the site has run through the Roth versus traditional choice, employer match vesting and HSA investment placement. Same dollar, different container, different result.
So where does the difference actually get created?
Taxable account vs Roth IRA: where the gap comes from
The wrapper does not change the fund. It changes whether each year’s dividend is taxed before it is reinvested.
Inside the Roth, the whole dividend goes back to work. In the taxable account, the model pays the federal tax out of that dividend first, then reinvests what is left. At a constant 15 percent, fifteen cents of every dividend dollar stops compounding inside the account.
In year one, that tax barely looks worth discussing. A 2 percent yield taxed at 15 percent is about 0.3 percent of the balance. That is exactly why it is easy to ignore.
A dividend only gets the preferential rate when the requirements are met, including the qualified-dividend holding period. After that, filing status and taxable income determine the band. For a single filer in 2026, the maximum zero-rate amount is $49,450 and the maximum 15-percent-rate amount is $545,500. Qualified dividends and long-term gains stack on top of other taxable income, so those thresholds are not separate allowances. They are 2026 figures; the model holds one rate for thirty years because it is an illustration, not a forecast.
The second tax, thirty years later
The after-tax dividend joins basis, so it is not taxed twice. Everything above basis is. When the model sells the taxable position at year 30, that bill arrives all at once.
Whether Theo holds an ETF or a mutual fund changes nothing here because capital-gain distributions are excluded from the model. In a real taxable account they are not excluded, and the two structures can distribute gains differently. ETFs and mutual funds differ on distributions, which is its own comparison.
Commissions are not the culprit either. A positive tax rate creates drag at a zero-commission broker just as easily, whatever other costs that broker carries.
None of this is dramatic in any single year. That is the whole problem. You can watch what a small annual drag does to a compound curve if the arithmetic is easier to see than to read.
How $874 became $73,520
Run both columns side by side and the separation is almost invisible at first.
| Year | Roth IRA balance | Brokerage, net of sale tax |
|---|---|---|
| Year 5 | $38,712 | $37,838 |
| Year 10 | $88,800 | $84,732 |
| Year 15 | $159,051 | $148,301 |
| Year 20 | $257,582 | $234,930 |
| Year 25 | $395,777 | $353,452 |
| Year 30 | $589,601 | $516,082 |
Five years in, the gap is $874, small enough to dismiss. By year 20 it is $22,652, even though Theo has only repeated the same deposit decision.
The first five years of this model produce $874 of separation. The last five add $31,195. The tax rate does not rise; the balance exposed to it does.
Thirty years of the same deposits in the same fund leave $589,601 in the Roth path and $516,082 in the taxable path after the assumed sale. The difference is $73,520.
Method in brief: Think of the exercise as a matched-pair test rather than a forecast. Theo’s deposit schedule and investment performance are cloned across two columns. Only the federal-tax wrapper varies. One column keeps distributions sheltered; the other trims distributions as they arrive and settles appreciation at the ending liquidation. At year 30 both are compared as spendable amounts. Earlier Roth checkpoints are accumulation balances, not estimates of cash from a full early withdrawal. State levies, NIIT, product expenses, inflation and fund-level capital-gain payouts are omitted. Read the result as a mechanism check under fixed eligibility, tax-rate and exit assumptions, not as a personal projection.
At 70, the modeled Roth distribution adds nothing to Theo’s taxable income. The taxable path hands him a tax bill on the way out.
Where the next dollar goes
This only applies to money you have already decided to invest for the long term, after the cash reserve, employer-plan and debt questions are settled. Inside that narrower choice, the sequence is short.
Work out what you are actually allowed to put in a Roth this year. Determine the permitted Roth amount for the contribution year using compensation, modified AGI and the combined traditional-and-Roth IRA limit. Use the IRS contribution-limit calculation with the thresholds for that tax year; the linked 2025 publication has a separate 2026 update. Other IRA contributions count once toward the combined limit. After working out the permitted Roth amount, subtract only Roth contributions already assigned to that year to find your remaining Roth contribution room. It is not automatically $7,500.
For 2026 the general cap is $7,500, or $8,600 if you reach 50 by year end. A single filer or head of household phases out between $153,000 and $168,000 of modified AGI. You can still assign a contribution to tax year 2026 up to the due date of the 2026 return, excluding extensions. After that, the unused room is gone; it does not roll forward.
Then send the next eligible dollar there until the room is used. Taxable takes the overflow when nothing else has a stronger claim on it. When you set up an automatic deposit, name the destination on purpose. An unchanged setting made the choice for Theo.
A taxable brokerage account has no cap and no phase-out, so it can hold whatever does not fit. It also has no age rule on withdrawals. Unrestricted access does not protect a volatile fund from a market loss, so money with a firm date still needs an investment that matches its horizon. Cash parked there earns whatever your brokerage sweep account rate happens to be, and a loss inside it may be usable against other gains under the tax-loss harvesting rules, which an IRA does not offer. If you later sell only part of a position with multiple lots, tax-lot selection can change which basis and holding period enter that sale.
A bank sweep can also change whether SIPC or FDIC applies to that cash.
Taxable accounts can be cash or margin; that permission choice is separate from the tax wrapper.
When Roth-first may not fit
The scenarios below show how tax rates and holding periods change the gap.
If you read one row, read the zero-rate row. It is the only case where the answer flips to a tie.
| Scenario | Roth IRA | Brokerage, net of tax | Gap |
|---|---|---|---|
| Base: 15% rate, 30 years | $589,601 | $516,082 | $73,520 |
| Constant 0% rate | $589,601 | $589,601 | $0 |
| Constant 20% rate | $589,601 | $492,678 | $96,924 |
| 20-year horizon | $257,582 | $234,930 | $22,652 |
| 40-year horizon | $1,242,734 | $1,047,707 | $195,027 |
Full sensitivity table (11 rows, including return and contribution variations)
Sensitivity of the thirty-year gap to one changed assumption at a time
| Row | What changed | Roth IRA | Brokerage, net of tax | Gap | Change vs BASE |
|---|---|---|---|---|---|
| BASE | return 7% / dividend 2% / rate 15% / horizon 30y / contribution $6,000 a year / opening balance $3,000 | $589,601 | $516,082 | $73,520 | baseline |
| R1 | total return 5.0% (dividend 1.5% / price 3.5%) | $411,599 | $372,337 | $39,261 | -$34,258 |
| R2 | total return 9.0% (dividend 2.5% / price 6.5%) | $857,648 | $729,046 | $128,603 | +$55,083 |
| R3 | dividend yield 1.0% (price 6.0%) | $589,601 | $522,274 | $67,328 | -$6,192 |
| R4 | dividend yield 3.5% (price 3.5%) | $589,601 | $507,059 | $82,543 | +$9,023 |
| R5 | constant qualified-dividend and long-term rate 0% for the full horizon | $589,601 | $589,601 | $0 | -$73,520 |
| R6 | constant qualified-dividend and long-term rate 20% for the full horizon | $589,601 | $492,678 | $96,924 | +$23,404 |
| R7 | horizon 20y (Theo at 60; qualified Roth distribution) | $257,582 | $234,930 | $22,652 | -$50,868 |
| R8 | horizon 40y (Theo at 80) | $1,242,734 | $1,047,707 | $195,027 | +$121,507 |
| R9 | constant $7,500 annual contribution (equal to the 2026 under-50 cap) | $731,293 | $640,357 | $90,935 | +$17,415 |
| R10 | contribution $3,000 a year | $306,219 | $267,530 | $38,689 | -$34,831 |
R5 confirms the mechanism. Set the rate on every modeled dividend and the terminal gain to zero, and the two paths land on the same number. The modeled advantage comes from the tax drag the Roth avoids.
Three situations deserve a second look before you automate anything.
Your applicable rate is zero. For a single filer in 2026, qualified dividends and long-term gains can fall partly or entirely within the 0 percent band when taxable income, including those dividends and gains, stays within the applicable threshold. Because gains stack on top of ordinary taxable income and future thresholds are unknown, check the actual return rather than assuming the zero-rate row applies for decades.
The money has a date on it. Roth withdrawals depend on what is being withdrawn: regular contributions, conversions and earnings each follow different rules. If a home purchase or another expense has a firm date, compare the required cash against liquid reserves and remaining contribution basis first. Do not treat conversions or earnings as equally reachable.
You are drawing down, not adding. That is a withdrawal-order problem. This model answers a contribution-order question, and the two do not use the same logic.
The decision that repeats
The account label matters less than the repeated deposit destination. In this model, the same choice is made thirty times, and the arithmetic keeps score.
By year 30, Theo has put in $183,000 of regular contributions along the Roth path: the opening $3,000 plus thirty deposits of $6,000.
Those are the dollars IRS ordering rules treat as coming out first, and returns of regular contributions are not included in gross income. The figure assumes each deposit was a permitted regular contribution in its assigned tax year and that Theo made no earlier withdrawals.
For money already cleared for investing: check what you have assigned to this tax year, work out the room that is left, and name the destination of the next deposit yourself.
Among households that owned a traditional or Roth IRA in mid-2025, 62 percent made no contribution for tax year 2024. ICI also reports why: retirement, no room to save, a workplace plan that already covers it, eligibility limits. Theo is none of those. He had the $6,000, he had the eligibility, and he had until the filing deadline. He just never changed where the money landed.
The dividend tax underneath all of this has its own arithmetic. Here is what dividend tax drag costs over a long hold.
The contribution window closes with the amount you actually put in, not the amount you intended to add later.
Before your next deposit
Check which account is selected and whether that destination still matches the money’s time horizon and your remaining Roth room.
Frequently asked questions
Is an IRA a brokerage account?
An IRA is an account type a brokerage firm can hold for you. Both accounts can sit at the same firm, hold the same index fund and appear on the same login. The account type controls the tax rules. The IRA modeled in this article is a Roth IRA; a traditional IRA is taxed differently on the way out and needs its own analysis.
Can I take money out of a Roth IRA early?
Regular Roth contributions are treated as distributed first and are not included in gross income. Conversions and earnings follow separate tax and penalty rules. In the model above, $183,000 is contribution basis, but that does not make the whole balance freely available. If early access is the actual plan, compare the expense against liquid savings and remaining basis first.
Can I fund an IRA and a brokerage account in the same year?
Yes. The Roth has an eligibility-dependent annual limit; the taxable account has none. For long-term dollars, use the calculated Roth room first when the conditions here fit, then consider taxable alongside your other options. If a direct Roth contribution is reduced or unavailable, traditional-IRA and conversion routes require a separate tax analysis.
Update history
- Date correction2026-10-31CORRECTION
Corrected the original publication date to July 30, 2026 to match the publishing record, and updated the author title. No analysis, figure, or source changed.
- Independent-check clarificationOctober 17, 2026CLARIFICATION
Described the sensitivity scenarios without implying a general ranking across inputs, and removed an unsupported claim about what readers assume. Tax rules, model inputs and all calculated values are unchanged.
- Article clarificationOctober 17, 2026CLARIFICATION
Clarified the two counterfactual deposit paths in the opening, reproduced the account recursions and sensitivity values, and replaced unsupported personal-work assertions with the objective method. Consolidated source strips; all model tables and original links are preserved.
- 2026-10 verification2026-10-15CORRECTION
Clarified the prior-year opening contribution and first annual deposit, labeled early Roth checkpoints as balances rather than full early-withdrawal cash, and separated the remaining-room steps to avoid double subtraction. Model values are unchanged.
- 2026-10 review 2026-10-15 UPDATE
Clarified the Roth-specific scope of the title and opening, and repaired a missing space at the contribution deadline. Preserved the earlier October 15 layout and image corrections and all modeled values.
- 2026-10 repair2026-10-15CORRECTION
Removed repeated account-permission text and improved the data-table label alignment and featured-image footer spacing.
- Historical entry 1July 30, 2026HISTORY
: Published.
- Historical entry 2July 31, 2026HISTORY
: Restructured. The opening now separates the statement-balance gap from the post-liquidation gap, the main sensitivity table shows five decision-relevant rows with the full eleven available on expand, and the model convention for paying dividend tax is stated more precisely. A concise method now sits beside the governed result, while the reproducible full method remains in the bottom trust package. The ending now includes a direct pre-deposit check. No calculated figures changed.