Step-Up Basis: The Tax Rule That Saves Families $50K–$200K (And How to Document It)

Most families discover step-up basis the same way: a CPA mentions it three weeks before they sell the inherited house, and they realize they should have done something six months earlier.

Step-up basis is one of the most beneficial provisions in the Internal Revenue Code — and it's also one of the most procedurally fragile. The benefit only fully applies if you can document the fair market value at the date of death. Without documentation, the IRS may default to a much lower basis, and the family pays capital gains tax on appreciation that should have been excluded.

Here's what every adult should know.

The mechanism, in 90 seconds

Under IRC §1014, when you inherit property, your cost basis is "stepped up" to the fair market value at the date of death of the original owner. This means when you eventually sell, you only owe capital gains tax on the appreciation that occurred AFTER the date of death — not on the lifetime of appreciation from when the original owner purchased the property.

The math, with a real example

Your mother bought a house in 1985 for $80,000. She made $40,000 in capital improvements over 35 years, bringing her adjusted cost basis to $120,000. She passes away in 2024 with the house worth $850,000. You inherit the house.

Six months later you sell it for $880,000.

Without step-up basis (the wrong way):

Sale price: $880,000
Cost basis: $120,000 (your mother's adjusted basis, the wrong basis to use)
Capital gain: $760,000
Federal long-term capital gains tax (assume 20% bracket): $152,000
Net Investment Income Tax (3.8%): $28,880
California state tax (assume 9.3%): $70,680
Total tax: ~$251,560

With step-up basis (the correct way):

Sale price: $880,000
Cost basis: $850,000 (stepped-up to date-of-death FMV)
Capital gain: $30,000
Federal long-term capital gains tax (20%): $6,000
NIIT (3.8%): $1,140
California state tax (9.3%): $2,790
Total tax: ~$9,930

Same house. Same sale. Difference: $241,630.

That's not a rounding error. That's the difference between a family paying off a mortgage and a family losing a year of expected retirement.

The documentation problem

The math above only works if you can prove the date-of-death FMV. The IRS won't take your word for it. The standard documentation is a licensed real estate appraisal performed by a qualified appraiser, with the valuation date set explicitly to the date of death.

Three things matter here:

The appraisal must be qualified. A casual Zillow estimate or a Realtor's comparative market analysis (CMA) is not a "qualified appraisal" for IRS purposes. You need a licensed appraiser issuing a formal report.
The valuation date must be the date of death. Not the date of inheritance. Not the date of distribution from the estate. The date the original owner died.
The timing matters. Order the appraisal within 6 months of the date of death. Appraisers can do retroactive valuations later, but it gets harder to defend on audit as time passes. The market data the appraiser uses must be from the period around the date of death.

Cost of a qualified date-of-death appraisal: typically $400–$600 for a single-family home. Cost of NOT having one when the family eventually sells: typically $50,000–$250,000+ in unnecessary tax.

Alternative valuation date election

For estates large enough to file Form 706 (the federal estate tax return), the executor can elect to use a date 6 months after the date of death instead of the date of death itself. This is useful only if asset values dropped during that 6-month window.

The election applies to the ENTIRE estate, not individual assets. The election must be made on Form 706 and is irrevocable. Talk to a CPA before electing.

Community property states get a "double step-up"

In the 9 community property states (CA, TX, AZ, NV, WA, ID, NM, WI, LA), when one spouse dies, BOTH halves of the community property get a step-up in basis — including the surviving spouse's half.

This is a major tax advantage and is a key reason why community-property states are particularly attractive for retirees with significant appreciated assets. In non-community-property states, only the deceased spouse's half gets the step-up; the surviving spouse retains their original basis on their share.

Example: a California couple owns a house bought for $200K, now worth $1.2M. When one spouse dies, the entire $1.2M becomes the surviving spouse's new basis. If the survivor sells immediately, ~$1M of appreciation is wiped out for tax purposes.

In a common-law state like Massachusetts, the same situation would result in only the deceased's $500K half getting stepped-up. The survivor would still owe capital gains on their $500K share over the original $100K (their half of the basis).

What doesn't get a step-up

Step-up basis does not apply to:

Inherited Traditional IRAs and 401(k)s. These are tax-deferred accounts. Distributions are taxed as ordinary income to the beneficiary. No step-up.
Inherited Roth IRAs. No step-up needed — distributions are already tax-free if the 5-year holding period was met by the original owner.
Property in irrevocable trusts (most cases). Depends on the trust structure. Property in a revocable trust does get a step-up at the grantor's death. Property in an irrevocable trust generally does not unless it's includible in the grantor's gross estate for estate tax purposes.
Gifted property (during the giver's lifetime). Lifetime gifts use carryover basis, not stepped-up basis. This is one reason families should usually NOT gift highly appreciated property during their lifetime — let it pass at death to capture the step-up.

Action checklist

If you've recently inherited appreciated property (real estate, business interests, investments):

Order a qualified date-of-death appraisal within 6 months. Cost: $400–$1,200 depending on property complexity.
For inherited investment accounts: request a "step-up basis report" from the brokerage. Most major custodians can issue one on request.
Save the documentation permanently. You will need it whenever you eventually sell. Without it, your basis is whatever the IRS decides — usually the worst possible answer.

If your parents own appreciated property and you may inherit:

Discourage lifetime gifts of appreciated property. They lose the step-up.
Encourage Roth conversions if Traditional IRAs are part of the estate. Roth IRAs pass to heirs tax-free.
If parents live in a non-community-property state, discuss whether moving to a community-property state in retirement makes sense for tax purposes. (Usually it doesn't — but worth thinking through.)

The step-up basis worksheet at /tools/estate-inventory walks through the documentation for each asset type. The cost-of-waiting calculator at /tools/cost-of-waiting shows what families lose when they don't act.