If a big share of your net worth sits in one company’s stock, whether from RSUs, early-employee equity, or founder shares, you’ve probably been told to diversify and hit the same wall: selling means a large tax bill. A 351 exchange is a lesser-known way around that wall, and for the right person it’s one of the better options out there. The catch is in who counts as the right person.
Most concentrated investors know the risk and still don’t move
A single stock holding a large share of your wealth ties your future to one company. If it has a bad run, it can take a deep bite out of your net worth, and a stock that falls can stay down for years.
Most people who know this still wait. Selling to diversify means a capital gains bill that can top 30% in a high-tax state, and that friction, plus plain inertia and faith in the stock, keeps them in place.
It helps to split this into two problems
The concentration and the tax bill are not the same issue, even though they always show up together. One problem is how much of your wealth rides on a single name. The other is how to reduce that without handing an unnecessary share to the IRS.
Keeping them separate clarifies what each tool is for. A 351 exchange is built for the latter.
A 351 is basically a no-sale rebalance (with some quirks).
A 351 exchange works like a potluck. You and a group of other investors each bring a dish to the table, your appreciated stock being your contribution, and rather than leaving with the plate you walked in with, everyone shares in the full spread.
In practice, you contribute your shares into a newly launched ETF and receive fund shares of equal value. Because you brought your stock to the table instead of selling it at the door, no capital gains are triggered at the time of the swap.
That is the appeal: your whole position keeps compounding instead of losing a slice to tax on the way to diversifying.
The tax isn’t erased, though. Your original cost basis carries into the ETF, so you’d still owe the gain if you later sold the fund shares, and it disappears only through the step-up at death. This is also why a 351 only applies to stock held in a taxable account: inside an IRA or 401(k) you can already rebalance without a tax bill, so there’s nothing to solve.
A 351 diversifies a portfolio, not a single position
That single fact decides whether the strategy is available to you. What you contribute has to clear a diversification test as a whole before it reaches the fund.
The test is the 25/50 rule: no single holding can be more than 25% of what you contribute, and your five largest holdings together can’t be more than 50%.
Index funds help more than you’d expect, because an ETF is counted as the stocks inside it rather than as one position. An S&P 500 fund isn’t a single 40% holding; it’s hundreds of small ones. So holding index funds next to your concentrated stock pulls your single-name weight down.
Say you have $1M: $200k in your employer’s stock, $500k in an S&P 500 fund, $200k spread across a few other names, and $100k in cash. The employer stock is 20% of the basket, the index fund dissolves into the hundreds of stocks it owns, and no single name comes near 25%. That portfolio clears the test.
So the question that decides fit is whether your whole contributed basket passes 25/50, not whether you feel concentrated. Once you count the index funds, the other holdings, and the cash, more people clear it than the word “concentrated” suggests.
A couple more rules shape what you can bring
You can only contribute securities you already own outright, so vested shares and other holdings count, while unvested RSUs and unexercised options don’t.
There’s also a rule that the group seeding the new ETF has to own at least 80% of it right afterward. The sponsor handles that by pooling contributors, so it isn’t something you manage.
What if one position still dominates everything?
You don’t have to contribute the entire position. You contribute as much of it as keeps it under 25% of the basket, so a heavily concentrated holder can still put in a slice alongside their other holdings and get partial diversification.
The trouble is how small that slice gets. If 90% of your wealth is in one stock, only a sliver clears the 25% line, so a 351 diversifies a little at a time and isn’t a strong fix for the whole position.
When a 351 can’t do much for you, the most straightforward route is to sell down over several years on a capital gains budget: realize a set amount of gain each year to keep the bill in a bracket you’re comfortable with, and harvest losses elsewhere to offset some of it. Paying some tax to get diversified is a reasonable trade, and often the simplest one. An exchange fund is a more exotic option for extreme concentration, though it locks you up for around seven years and requires accredited status.
So how does a 351 actually happen?
Sponsors like Cambria and Alpha Architect run these conversions. They vet your basket against the rules, pool contributors, and seed the new ETF, all within a set window tied to the fund’s launch.
The cost is low and the result is liquid. These funds typically run around half a percent a year, and unlike an exchange fund, you can sell your ETF shares whenever you want.
Going in means committing to the fund, not just the tax move
When you contribute, you trade your hand-picked positions for the ETF’s strategy, so the swap only makes sense if you actually want to own that fund.
And because this is deferral rather than forgiveness, a 351 fits best when you plan to hold the diversified fund for the long haul. Selling soon after just surfaces the gain you postponed.
Whether a 351 fits comes down to three questions
It comes down to whether your contributed basket clears 25/50, whether you want to own the fund you’d end up in, and whether you’ll hold it for the long term rather than selling soon after.
If those three line up, a 351 is one of the better options available for getting diversified without a tax bill. Figuring out whether your basket qualifies, which fund fits, and how to time it against a launch window is something we help our clients with: stoneholtwealth.com/get-started.
This article is for educational purposes only and is not investment, tax, or legal advice. Investing involves risk, including possible loss of principal. Concentrated stock positions, 351 exchanges, exchange funds, and other diversification strategies carry their own risks and tax consequences and may not be appropriate for every investor; a 351 exchange defers tax rather than eliminating it. Examples are hypothetical and for illustration only; they do not represent results achieved by any Stoneholt client. Consult a qualified professional about your specific situation.
