Inherited Stock Capital Gains: Stepped-Up Basis Rules

An heir who inherits $400,000 of stock their parent bought for $40,000 owes capital gains tax on almost none of it. The $360,000 of appreciation that built up over the parent’s lifetime disappears for tax purposes the moment the original owner dies. That single mechanic — the stepped-up basis under Internal Revenue Code §1014 — is the most valuable, least understood provision in the capital gains code for high-net-worth families.

The rule is simple to state and easy to mishandle. When you inherit a capital asset, your cost basis resets to the asset’s fair market value on the decedent’s date of death rather than what they originally paid. Sell immediately and your taxable gain is close to zero. Hold for years and you only owe tax on appreciation after the death — never on the gain that accrued during the decedent’s life.

The numbers that matter

Sources: IRS Topic No. 409 (2025); IRS Publication 551, Rev. December 2025; IRS Instructions for Form 8949 (2025); IRC §1411.

Two of those rows deserve emphasis because they cut against intuition. The basis reset is not a discount or a deferral — it is a permanent erasure of pre-death appreciation. And the holding-period rule means an heir who sells inherited stock the week after probate clears still gets long-term capital gains (LTCG) treatment, even though they held the shares for days. The IRS instructions for Form 8949 are explicit: property acquired by inheritance is reported as a long-term gain or loss regardless of actual holding time.

How the step-up actually erases tax

Work through the mechanics with a concrete position. Suppose a parent bought $50,000 of a single stock in 1998. By their death in 2025 the position is worth $250,000. The embedded gain is $200,000.

Had the parent sold the day before dying, that $200,000 would have been a taxable long-term gain. At a 15% federal rate plus the 3.8% net investment income tax (NIIT), the bill would run roughly $37,600. Instead, the parent dies holding the stock. The heir’s basis steps up to the $250,000 date-of-death value. If the heir sells at $250,000, the reported gain is zero, and the tax is zero. The entire $200,000 of lifetime appreciation escapes income tax permanently.

The step-up is not always favorable. If an asset has lost value, §1014 produces a stepped-down basis to the lower date-of-death figure, and the heir forfeits the ability to claim that pre-death decline as a loss. IRS Publication 551 (Rev. December 2025) describes the rule as working in both directions: basis becomes fair market value at death whether that figure is higher or lower than the decedent’s original cost. For appreciated portfolios — which is most long-held equity — the rule is a windfall. For underwater positions, it destroys a deductible loss the decedent could have harvested while alive.

The cleaner planning point is this: an aging investor sitting on a large embedded gain and an aging investor sitting on an embedded loss face opposite incentives. The first should generally hold; the second should generally sell and harvest before death. This is the inverse logic of ordinary tax-loss harvesting math, applied across a lifetime rather than a tax year.

What the heir owes when they finally sell

The step-up does not make inherited stock tax-free forever. It resets the meter. Any appreciation after the date of death is a taxable gain when the heir sells, taxed at standard LTCG rates because of the automatic long-term treatment.

Consider an heir in the 15% federal bracket who inherits stock at a $250,000 stepped-up basis, holds three years, and sells at $310,000. The taxable gain is $60,000 — only the post-death growth. The pre-death $200,000 stays gone. The table below runs that sale across three scenarios that bracket where most $150k+ households land.

Sources: IRS Topic No. 409 (2025); IRC §1411 (NIIT). Mid-income heir assumes taxable income under $533,400 single but MAGI over the $200,000 NIIT threshold; top-bracket heir assumes taxable income over $533,400. Federal only; state tax excluded.

Two figures in that table apply only when MAGI clears the NIIT line. An heir whose total income stays under $200,000 (single) or $250,000 (married filing jointly) pays the 3.8% surtax on none of the gain. For a household already earning $150k+ in wages, a $60,000 gain stacked on top almost always pushes past the threshold, so the surtax is the realistic case rather than the exception. The mechanics of where that 3.8% line falls are covered in detail in the breakdown of the NIIT capital gains threshold.

State tax is where the bill diverges

Federal treatment of inherited stock is uniform nationwide. State treatment is not, and for high earners the state layer often exceeds the NIIT. Most states tax capital gains as ordinary income with no preferential long-term rate, so the post-death gain an heir realizes gets taxed at the state’s full marginal schedule.

California sits at the extreme. It applies its ordinary income brackets — 1% to 13.3%, the top rate reflecting a 12.3% bracket plus a 1% Mental Health Services Tax on income above $1 million — to all gains with no long-term carve-out. A high-income heir in California can face a combined federal-plus-state-plus-NIIT rate north of 37% on the post-death portion of an inherited-stock sale. The structural reasons California lands highest are unpacked in the analysis of California capital gains tax, and the full state-by-state spread appears in the capital gains tax by state comparison.

Nine states impose no individual income tax at all, meaning an heir there owes only the federal layer on post-death appreciation. The same $60,000 post-death gain that costs a top-bracket California heir roughly $22,000 all-in costs a Texas or Florida heir $14,280. Residency on the date of sale, not the date of death, generally controls which state taxes the gain — a planning lever that matters when an estate takes years to settle.

Finluxy After-Tax Gain Rate

The headline gain rate on inherited stock overstates what an heir keeps, because it ignores the tax on post-death appreciation and the state layer. The Finluxy After-Tax Gain Rate isolates the real retained return: net gain after all applicable taxes, divided by the heir’s stepped-up basis, expressed as a percentage. Compared against the pre-tax gain rate, the gap is the tax haircut.

Applied to the three-year hold from $250,000 to $310,000 — a 24% pre-tax gain on the stepped-up basis — the metric shows how much the heir’s location and bracket eat into that return.

Sources: IRS Topic No. 409 (2025); IRC §1411; California Franchise Tax Board 2025 brackets via Tax Foundation. Gain rates computed on $250,000 stepped-up basis. California row applies the 13.3% top marginal rate to the full gain for illustration; actual state tax depends on where the gain lands across brackets.

The metric reframes the decision. A 24% nominal gain becomes a 15.1% retained gain for a top-bracket California heir — an 8.9-point haircut driven almost entirely by the state and surtax layers, since the federal LTCG portion alone would cost about 5.7 points. The pre-death appreciation, by contrast, carries a zero-point haircut because the step-up erased it. That contrast is the whole game: the tax system treats lifetime gains and post-death gains as entirely different animals.

The overlooked insight: the basis-documentation gap

Most coverage of inherited stock stops at “your basis steps up.” The data point that gets lost is that the step-up is only as good as the heir’s proof of the date-of-death value — and for a single stock that figure is rarely documented automatically.

Brokerages report cost basis to the IRS on Form 1099-B, but for inherited securities the reported basis is frequently blank, wrong, or carried over from the decedent’s original purchase. If an heir sells and the 1099-B shows the decedent’s $50,000 basis instead of the $250,000 stepped-up figure, the heir who does not correct it on Form 8949 effectively pays tax on $200,000 of gain that the law erased. IRS Publication 551 stresses contemporaneous documentation — brokerage statements showing the security’s value on the exact date of death — precisely because reconstructing that figure years later invites scrutiny and penalties.

The dollar stakes of that paperwork gap are larger than the tax on most actual sales. A heir who fails to establish a $200,000 step-up overpays by roughly $30,000 to $40,000 in federal tax alone. The defensive move costs nothing: pull a date-of-death valuation the moment the account transfers, before the figure becomes hard to retrieve.

What a $150k+ household should actually do with this

For high-income families, the step-up reshapes two separate decisions, and they pull in opposite directions depending on which side of the inheritance you sit.

If you are the prospective decedent — an investor with a large, low-basis, appreciated position — the step-up is an argument against selling during your lifetime. Realizing a $500,000 embedded gain at the 23.8% top federal rate costs $119,000 that your heirs would never owe if you held the position until death. That changes the calculus on rebalancing a concentrated stock holding, and it interacts directly with the broader holding period tax cost framework: sometimes the optimal holding period is “until death.”

If you are the heir, the action item is timing and documentation, not avoidance. Because inherited stock is always long-term and the basis is fresh, there is rarely a tax reason to delay selling for diversification — selling immediately after a step-up generates little or no gain. The instinct to “hold what Mom left me” often concentrates risk for no tax benefit, since the tax advantage was already captured at the moment of death. For larger inheritances that push you firmly past the NIIT and into the 20% bracket, the relevant comparison is the full stock sale after-tax return across income levels, and for anyone weighing the broader gain landscape, the capital gains tax guide for $150k+ investors sets the full context.