Short answer: In a Roth IRA, an index fund’s dividends and gains aren’t taxed while they stay in the account, and qualified withdrawals are tax-free; in a taxable account, you pay tax on dividends every year and on gains when you sell, but there’s no contribution limit and you can withdraw at any time. For 2026, the IRS caps IRA contributions at $7,500 ($8,600 if you’re 50 or older), so many investors use both.
Once you’ve picked an index fund, there’s a second decision that can matter almost as much over a lifetime: which account you hold it in. The same fund, with the same returns, can leave you with noticeably different amounts after tax depending on whether it sits in a Roth IRA or a regular taxable brokerage account.
This guide compares the two for index fund investors: how each is taxed, what the limits are for 2026, and why many people use both. It’s general information, not tax advice; the right answer depends on your income, your goals and your tax situation.
If you’re still setting up your first account, our step-by-step guide on how to buy your first index fund covers the basics.
The short version
| Roth IRA | Taxable brokerage account | |
|---|---|---|
| Money goes in | After tax (no deduction) | After tax |
| Dividends and fund distributions | Not taxed while in the account | Taxed each year |
| Gains when you sell | Not taxed while in the account | Taxed when you sell at a gain |
| Withdrawals in retirement | Tax-free if they’re qualified distributions | Only the gains are taxed when you sell |
| 2026 contribution limit | $7,500 ($8,600 if 50 or older) | No limit |
| Income limits | Yes | No |
| Access before retirement | Restricted for earnings | Any time |
How a Roth IRA works
A Roth IRA is an individual retirement account with a simple deal: you pay tax on the money before it goes in, and in return, qualifying withdrawals later are tax-free.
The IRS summarizes the key points: “You cannot deduct contributions to a Roth IRA,” but “if you satisfy the requirements, qualified distributions are tax-free.” There’s no forced withdrawal while you’re alive, either: “You can leave amounts in your Roth IRA as long as you live” (IRS). The requirements for a qualified distribution generally involve reaching age 59½ and having had a Roth IRA for at least five years; the IRS explains the details in Publication 590-B.
For index funds, the effect is powerful. Every dividend the fund pays, every capital gains distribution and every dollar of growth stays inside the account, compounding without a tax bill, and comes out tax-free if you follow the rules.
The limits for 2026
- Contribution limit. For 2026, the IRS limit on IRA contributions is $7,500, plus an extra $1,100 catch-up for people aged 50 and over (IRS). That limit is shared across all your traditional and Roth IRAs.
- Income limits. Your ability to contribute directly to a Roth IRA phases out at higher incomes. For 2026, the IRS says the phase-out range is “between $153,000 and $168,000” for singles and heads of household, and “between $242,000 and $252,000” for married couples filing jointly (IRS).
- You need earned income to contribute, and you can’t contribute more than you earned in the year.
How a taxable brokerage account works
A regular brokerage account has no special tax treatment, but also no special rules. You can put in as much as you like and take money out whenever you want.
The trade-off is taxes along the way:
- Dividends are taxed each year, even if you reinvest them. Many dividends from U.S. stock index funds are “qualified” dividends, which can be taxed at the lower long-term capital gains rates.
- Capital gains distributions are taxed in the year the fund pays them, even if you didn’t sell anything.
- When you sell shares for more than you paid, the gain is taxed. The IRS explains that “if you hold the asset for more than one year before you dispose of it, your capital gain or loss is long-term. If you hold it one year or less, your capital gain or loss is short-term” (IRS). Long-term gains get lower rates: for 2026, 0%, 15% or 20%, depending on taxable income. A single filer pays 0% on long-term gains up to $49,450 of taxable income and 20% only above $545,500; for married couples filing jointly, the thresholds are $98,900 and $613,700 (IRS Rev. Proc. 2025-32).
There’s also an upside: losses can offset gains, and when you sell, only the gain is taxed, not the whole amount.
Why index funds suit both, but differently
Broad index funds are some of the most tax-efficient funds you can own in a taxable account. They trade little, so they rarely distribute large capital gains, and much of their return comes from price growth that isn’t taxed until you sell. Index ETFs can be even more efficient. Our comparison of index mutual funds and ETFs explains why, and our look at FXAIX, VOO and SWPPX shows what that has meant for three popular S&P 500 funds.
That efficiency means a taxable account is a perfectly good home for a broad stock index fund. But even a very tax-efficient fund pays dividends every year, and over decades those taxes add up. Inside a Roth IRA, they don’t exist.
A simple example
Imagine you invest $7,500 in a broad stock index fund and leave it for 30 years. Suppose the fund returns 7% a year in total, of which about 1.5 points are dividends. (These are illustrative assumptions, not a forecast, and real tax rates vary.)
- In a Roth IRA: the whole 7% compounds untouched. After 30 years, $7,500 grows to about $57,100, and a qualified withdrawal is tax-free.
- In a taxable account: suppose you pay 15% tax on the dividends each year, which trims the yearly return to about 6.78%. After 30 years, you’d have about $53,600. If you then sold everything and paid 15% on the gain, you’d keep roughly $46,700. (This simple example ignores that reinvested dividends raise your cost basis, which would reduce that final tax somewhat.)
The difference in this example, roughly $10,000 on a single $7,500 investment, comes entirely from taxes. The fund, the returns and the investor are the same.
When a taxable account makes sense
A Roth IRA isn’t always the right, or only, answer:
- You’ve already hit the contribution limit. With a $7,500 limit, many savers simply need somewhere else to put additional money.
- Your income is above the Roth limits. Direct Roth contributions phase out at higher incomes.
- You’ll need the money before retirement. A taxable account has no restrictions on withdrawals. In general, you can take out your own Roth contributions at any time, but earnings are a different story before you meet the rules.
- Flexibility matters. Money for a house, a business or a sabbatical may be better kept in a taxable account.
What about a 401(k) and a traditional IRA?
The Roth vs. taxable choice usually sits alongside a workplace plan. A common order many people follow is:
- Contribute enough to your 401(k) to get the full employer match, if there is one. For 2026, the 401(k) employee contribution limit is $24,500 (IRS).
- Then contribute to an IRA, Roth or traditional depending on your income and whether you expect your tax rate to be higher or lower in retirement.
- Then add more to the 401(k) or invest in a taxable account.
That’s a general pattern, not a rule. A traditional IRA or 401(k) gives you a tax break now and taxes withdrawals later; a Roth does the reverse. Which is better depends mostly on whether your tax rate is likely to be higher now or in retirement.
Using both: where to hold which fund
If you have both a Roth IRA and a taxable account, you don’t need to hold the same funds in each. You only need your overall mix to match your plan, a point we also make in our guide to the three-fund portfolio.
Some common tendencies:
- Bond index funds pay most of their return as interest, which is taxed as ordinary income in a taxable account. Many investors prefer to keep them in tax-advantaged accounts.
- Broad stock index funds are relatively tax-efficient and can work well in a taxable account.
- The Roth IRA is often used for the investments you expect to grow the most, because all of that growth can come out tax-free.
- International stock funds in a taxable account may let you claim a credit for foreign taxes the fund paid, which isn’t available inside an IRA.
These are general tendencies. Tax situations differ, and the simplest plan you’ll stick with beats a perfectly optimized one you won’t.
Common mistakes
- Leaving cash uninvested in the Roth IRA. Contributing to a Roth IRA puts cash in the account; you still have to buy the index fund.
- Trading often in a taxable account. Frequent selling turns long-term gains into short-term gains and creates tax bills. Index funds work best when left alone.
- Contributing more than the limit. Excess IRA contributions can trigger a penalty until they’re corrected.
- Ignoring fund costs. Tax savings are only part of the picture. A Roth IRA full of expensive share classes can still underperform. Our S&P 500 fee analysis shows how much costs vary for the same index.
Common questions
Can I hold the same index fund in both accounts? Yes. Many investors own the same broad index fund in a Roth IRA and in a taxable account. Just be careful if you sell a fund at a loss in the taxable account and buy it back in the IRA within a short period, because the wash-sale rules can disallow the loss.
Is a Roth IRA an investment? No. It’s an account, a kind of tax wrapper. What you actually own inside it are the investments you choose, such as an index fund. The account decides how they’re taxed; the fund decides what you own and what it costs.
Do ETFs make a taxable account as good as a Roth? Not quite. Index ETFs can avoid most capital gains distributions, but their dividends are still taxed every year, and you’ll owe tax on your gains when you sell. A Roth IRA avoids both, within its limits.
What if my income is too high for a Roth IRA? The direct contribution limits phase out at higher incomes. There are other routes some people use, but they come with their own rules and tax consequences, so it’s worth checking the IRS guidance or speaking with a tax professional before trying them.
Where should I start if I can only afford one? If you have a workplace plan with a match, that’s usually the first step. After that, for many people with eligible income and long-term goals, a Roth IRA holding a broad, low-cost index fund is a simple and tax-efficient next step. If you might need the money within a few years, a taxable account gives you more flexibility.
A quick decision checklist
- Am I getting any employer match in my 401(k)?
- Is my income within the Roth IRA limits for this year?
- Will I need this money before retirement?
- Have I already contributed the full $7,500 (or $8,600 if 50 or older) to IRAs this year?
- Do I expect my tax rate to be higher or lower in retirement than it is now?
The bottom line
A Roth IRA and a taxable account can hold exactly the same index fund, but they tax it very differently. The Roth lets every dividend and every dollar of growth compound without tax, within strict limits on how much you can put in and who can contribute. A taxable account has no limits and no restrictions, but taxes you along the way. For many investors, the answer isn’t one or the other: it’s filling the Roth IRA first, where they’re eligible, and using a taxable account for everything beyond it.
This article is general information, not tax, legal or investment advice. Tax rules and limits change and depend on your situation; check IRS guidance or speak with a tax professional. See our Financial Disclaimer.
Sources
- Internal Revenue Service, 401(k) limit increases to $24,500 for 2026, IRA limit increases to $7,500: 2026 contribution limits and Roth IRA income phase-out ranges.
- Internal Revenue Service, Roth IRAs: contributions, qualified distributions and lifetime rules.
- Internal Revenue Service, Topic no. 409, Capital Gains and Losses: long-term and short-term holding periods.
- Internal Revenue Service, Revenue Procedure 2025-32: 2026 long-term capital gains rate thresholds.
- Internal Revenue Service, Publication 590-B, Distributions from Individual Retirement Arrangements (IRAs): Roth IRA qualified distributions.
- The dollar example is our own calculation using hypothetical returns and tax rates.
Sources checked on September 30, 2026.