When a company you own spins off a subsidiary and drops new shares into your account, the stock spin-off tax rules and cost basis math generally work in your favor: the distribution itself is tax-free under Internal Revenue Code Section 355, but you have to split your original cost basis between the parent shares and the new shares based on their relative fair market values right after the distribution. Get that allocation wrong and you’ll overpay capital gains tax when you eventually sell.
Why the Distribution Is Tax-Free
Section 355 of the Internal Revenue Code says no gain or loss is recognized when a parent distributes stock of a controlled subsidiary to its shareholders, as long as the transaction meets several requirements. The main ones:
- Active business requirement. Both the parent and the new company must be actively conducting a trade or business immediately after the distribution, and that business must have been actively operated for at least five years before the distribution date.
- Not a device to distribute earnings. The transaction cannot be structured primarily as a way to funnel corporate profits to shareholders while disguising them as a tax-free distribution.
- Control before distribution. The parent must control the subsidiary immediately before the spin-off and must distribute all of its stock in the subsidiary, or enough to constitute control under Section 368(c), with the IRS satisfied that retaining any shares isn’t motivated by tax avoidance.
Large public spin-offs almost always clear these hurdles, and the parent typically secures a private letter ruling from the IRS confirming qualification before the deal closes.
How to Allocate Your Cost Basis
This is where most shareholders slip up. Receiving the new shares doesn’t leave your original basis in the parent untouched. You have to split that basis between the parent shares you still hold and the new shares you just received, in proportion to the two stocks’ fair market values right after the distribution.
An example. You bought 100 shares of the parent at $50, so your total basis is $5,000. After the spin-off, the parent trades at $40 and the new company trades at $10. The parent represents 80% of the combined value and the new company represents 20%. Your adjusted basis in the parent becomes $4,000, and your basis in the new shares becomes $1,000.
The parent company typically files IRS Form 8937 with the specific allocation percentages, and most brokerages apply those figures automatically. Verify the numbers yourself against Form 8937 before you rely on what shows up in your account.
Multiple Purchase Lots
If you bought parent shares at different times and prices, you cannot average your basis across all shares and then allocate. The IRS requires a lot-by-lot allocation: apply the same fair market value percentages to each separate purchase lot individually. Each lot keeps its own acquisition date and gets its own adjusted basis in both the parent and the new company.
Fractional Shares Paid in Cash
When the distribution ratio doesn’t divide evenly into your holdings, your broker aggregates the leftover fractions across shareholders, sells them on the open market, and sends you cash. That cash is the one piece of the spin-off that is immediately taxable. Treat it as proceeds from selling a fractional share and calculate your gain or loss using the allocated basis for that fraction.
Your Holding Period Carries Over
You don’t start a new clock on the spin-off shares. Under IRC Section 1223, when property has the same basis (in whole or part) as property you previously held, the holding period of the original property carries over, and Section 1223 specifically treats a Section 355 distribution as an exchange for this purpose. If you bought the parent three years ago, the spin-off shares are long-term holdings from day one. That matters, because long-term capital gains rates are meaningfully lower than short-term rates.
What Happens If the Spin-Off Fails Section 355
If the IRS determines a spin-off doesn’t satisfy Section 355, the consequences hit both sides. The parent owes tax on any built-in gain in the subsidiary’s stock. For shareholders, the distribution gets reclassified as a Section 301 distribution, meaning the full fair market value of the shares you received is treated as a taxable dividend to the extent of the parent’s earnings and profits.
That is a dramatically worse outcome than tax-free treatment, because you’d owe ordinary income tax on the entire value of the new shares rather than just reallocating your existing basis. The risk almost never materializes for large public spin-offs given the private letter ruling process, but it’s worth knowing what’s at stake.
Employee Stock Options and RSUs Are a Separate Matter
If you hold employee stock options or restricted stock units in the parent, the cost basis rules above don’t govern them. A spin-off triggers separate adjustments meant to preserve the economic value of your awards, and the specifics vary by company and by your equity plan.
For listed stock options, the Options Clearing Corporation issues adjustment memos that modify strike prices, contract sizes, or deliverables to reflect the spin-off. Check the OCC memo covering your specific contract rather than assuming your broker’s display is complete.
For unvested RSUs and performance shares, companies generally take one of a few approaches. Some convert all outstanding awards into equity of whichever company employs you after the separation. Others split awards into both parent and new-company equity at the same ratio as the stock distribution. A hybrid approach applies different methods depending on when the award was granted or when it vests. Most companies avoid forcing employees to forfeit unvested equity because of the restructuring alone.
Tax treatment of the adjusted awards generally follows the same rules as the original grants, but the adjustment has to be done correctly to keep compliance with IRC Section 409A (deferred compensation) and Section 424 (incentive stock option rules). This is the area of a spin-off where a tax advisor tends to earn the fee.
Spin-Offs vs. Split-Offs and Carve-Outs
The rules above apply to spin-offs specifically. Two related transactions look similar and get confused with them, but the tax mechanics differ.
A split-off is elective. You exchange some of your parent shares for shares of the subsidiary, and not every shareholder participates. Because you’re giving something up to receive the new shares, the analysis is different from an automatic pro-rata distribution.
An equity carve-out is a partial IPO. The parent sells a minority stake in the subsidiary to outside investors and keeps majority control. You don’t receive shares at all unless you buy them on the open market, and there’s no basis reallocation to worry about because nothing was distributed to you.
If a corporate action in your account is one of those instead of a true spin-off, the Section 355 framework and the basis-split formula don’t apply the same way. Read the transaction documents and any Form 8937 the company files before assuming the mechanics.