A credit shelter trust is an irrevocable trust funded when the first spouse dies that uses up that spouse’s federal estate tax exemption, keeping the sheltered assets (and everything they earn afterward) out of the surviving spouse’s taxable estate. Both spouses’ exemptions get used instead of one going to waste. For 2026, the federal basic exclusion amount is $15,000,000 per person, so a married couple can shield up to $30 million from federal estate tax with the right structure.1Office of the Law Revision Counsel. 26 USC 2010 – Unified Credit Against Estate Tax Whether the trust is worth setting up depends on more than that headline number.
How the Trust Actually Works
Nothing happens with a credit shelter trust while both spouses are alive. The trust document sits in the estate plan, dormant. When the first spouse dies, the estate splits in two.
One share, often called the A trust or marital trust, passes to the surviving spouse under the unlimited marital deduction, so no federal estate tax is owed on that portion. The other share, the B trust or credit shelter portion, is funded up to the value of the deceased spouse’s available exemption. The unified credit wipes out any estate tax on that transfer.1Office of the Law Revision Counsel. 26 USC 2010 – Unified Credit Against Estate Tax
The B trust then becomes irrevocable. The surviving spouse can benefit from it under specific rules, but doesn’t own the assets. Because the assets are not part of the survivor’s estate, they pass to the final beneficiaries (usually the children) without a second estate tax when the surviving spouse eventually dies. Any appreciation that happens inside the trust during those intervening years also escapes estate tax at the second death. That sheltered growth is where a lot of the trust’s long-term value comes from.
Why Anyone Still Uses One at a $15 Million Exemption
The One, Big, Beautiful Bill, signed into law on July 4, 2025, as Public Law 119-21, permanently set the basic exclusion amount at $15,000,000 per person starting in 2026, with annual inflation adjustments beginning in 2027.2Office of the Law Revision Counsel. 26 US Code 2010 – Unified Credit Against Estate Tax That replaced the temporary 2017 increase that had been set to sunset at the end of 2025 and drop the exemption back to roughly $7 million per person.3Internal Revenue Service. Whats New – Estate and Gift Tax The top federal rate on amounts above the exemption stays at 40%.
At those thresholds, a lot of couples will never owe federal estate tax whether they set up a credit shelter trust or not. But federal tax avoidance was never the only reason to build one. The trust still earns its place when any of the following applies:
- The couple lives in a state with its own estate tax. Roughly a dozen states and the District of Columbia impose one, with exemptions ranging from about $1 million to roughly $7 million. A trust funded up to the state exemption can shelter that portion from state estate tax at the second death, the same way it works federally.
- The couple wants to preserve both spouses’ generation-skipping transfer (GST) exemptions for grandchildren or dynasty-style planning. GST exemption is not portable between spouses; only a trust preserves it.
- The surviving spouse might remarry, face creditors, or go through a divorce. Assets inside the trust are generally shielded; assets inherited outright are not.
- The assets are expected to appreciate substantially. All that growth stays outside the survivor’s estate.
- There are children from a prior marriage whose inheritance needs to be locked in at the first death rather than left to the surviving spouse’s discretion.
How Portability Compares
Since 2011, there has been a simpler alternative called the portability election. When the first spouse dies, the executor files Form 706 and transfers the deceased spouse’s unused exclusion (the DSUE amount) to the survivor, who adds it on top of their own exemption.4Office of the Law Revision Counsel. 26 USC 2010 – Unified Credit Against Estate Tax It’s easier and cheaper than administering a trust, and for many moderate estates it’s enough. But portability has real limits.
The DSUE amount freezes at the value computed on the Form 706. It never adjusts for inflation, and the underlying assets, once inherited outright, grow inside the survivor’s taxable estate. Portability also does nothing for the GST exemption. And the DSUE is tied to the survivor’s last deceased spouse: if the survivor remarries and the new spouse dies first, the original DSUE can be lost. Outright inheritance offers no creditor or divorce protection. The IRS can also revisit the deceased spouse’s Form 706 indefinitely to verify the DSUE amount, so the executor’s records need to stay accessible for the rest of the surviving spouse’s life.
Portability works well for couples whose combined estate sits comfortably below the exemption, who live somewhere with no state estate tax, and who plan to leave everything to the same people. A credit shelter trust earns its keep when future appreciation, state tax, GST planning, or structural protection is on the table.
What the Surviving Spouse Can Access
The surviving spouse doesn’t own the trust assets, but a well-drafted credit shelter trust still supports them financially. Federal regulations allow distributions for an “ascertainable standard” without pulling the assets back into the survivor’s taxable estate. That standard covers health, education, support, and maintenance, often referred to as the HEMS standard.5eCFR. 26 CFR 20.2041-1 – Powers of Appointment; In General
Support and maintenance are not limited to bare necessities. The regulation specifically recognizes “support in reasonable comfort” and “maintenance in health and reasonable comfort.” What disqualifies a power is language broad enough to allow distributions for the holder’s general happiness or welfare with no objective benchmark. Trust documents typically direct the trustee to distribute all net income to the surviving spouse annually, with principal available for legitimate HEMS needs.
Giving the surviving spouse too much control creates a general power of appointment and collapses the tax benefit. If the survivor can withdraw funds for any reason without trustee approval, the IRS treats the trust assets as part of their estate. This is the single most common drafting mistake in credit shelter trusts, and it’s usually irreversible once the first spouse has died and the trust has become irrevocable.
The Step-Up in Basis Trade-Off
This is the part that catches families off guard. When the first spouse dies, assets moved into the trust receive a new tax basis equal to their fair market value at the date of death.6Office of the Law Revision Counsel. 26 US Code 1014 – Basis of Property Acquired From a Decedent That step-up eliminates embedded capital gains accumulated during the first spouse’s lifetime.
At the second death, though, the trust assets are not “acquired from a decedent” because the whole point was to keep them out of the survivor’s estate. They don’t get a second step-up. If the assets have appreciated a lot between the two deaths, the beneficiaries inherit the first-death basis and owe capital gains tax on all that growth when they sell.
Under a straight portability plan, by contrast, the surviving spouse inherits everything outright, and at the survivor’s death every asset gets a fresh step-up to current fair market value. Beneficiaries then sell with no built-in gain. For a family whose wealth sits in rapidly appreciating assets (real estate in a strong market, a growing business), the lost second step-up can cost more in capital gains tax than the trust saves in estate tax. That math has only gotten harder to justify as the federal exemption has climbed. Any plan built around a credit shelter trust should model both sides before locking the structure in place.
What Happens When the First Spouse Dies
The trust is drafted while both spouses are alive. Attorney fees typically run from $2,500 to $7,500 or more, depending on the complexity of the estate. The document names the trustee, identifies the remainder beneficiaries, spells out the HEMS distribution rules, and includes the funding formula that determines how much moves into the B trust at the first death.
At the first death, the trustee retitles the deceased spouse’s assets into the name of the trust: new deeds recorded at the county level for real estate, ownership changes at each institution for brokerage and bank accounts. The trustee also applies for an Employer Identification Number through the IRS using Form SS-4 or the online EIN application; that number becomes the trust’s tax ID.7Internal Revenue Service. Instructions for Form SS-4 – Application for Employer Identification Number
The executor files Form 706, the United States Estate and Generation-Skipping Transfer Tax Return, to report the total gross estate, claim the marital deduction for whatever passes to the A trust or surviving spouse, and apply the unified credit against the B trust allocation.8Internal Revenue Service. Instructions for Form 706 – United States Estate and Generation-Skipping Transfer Tax Return Accurate date-of-death valuations matter because those figures set the new cost basis for every asset in the trust. Form 706 is due within nine months of death, with a six-month filing extension available through Form 4768 (though any tax owed is still due at nine months).
Ongoing Trust Income Taxes
Once funded, the trust is its own taxpayer. The trustee files Form 1041 every year the trust has gross income of $600 or more or any taxable income, due April 15 for a calendar-year trust.9Internal Revenue Service. Instructions for Form 1041 and Schedules A, B, G, J, and K-1
Trust income tax brackets are heavily compressed. For 2026, trust income hits the top 37% rate at just $16,000 of taxable income, while an individual filer doesn’t reach that bracket until hundreds of thousands of dollars.10Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026, Including Amendments From the One, Big, Beautiful Bill That creates a strong incentive to distribute income to the surviving spouse rather than let it accumulate inside the trust. When income is distributed, the trust deducts it and the beneficiary reports it on their personal return at their (usually lower) individual rate. Most credit shelter trusts require annual income distributions for exactly that reason.
The trustee also issues Schedule K-1 to each beneficiary who receives a distribution, keeps records of income, expenses, and distributions, and pays estimated taxes on anything the trust retains. Professional or corporate trustees typically charge an annual fee in the range of 0.4% to 2% of assets under management. That recurring cost belongs in the decision to use this structure at all.
When It Fits and When It Doesn’t
With the federal exemption permanently at $15 million per person, fewer families have a federal estate tax problem to solve. But the credit shelter trust was never only an estate tax tool. It still fits when the couple lives in a state with its own estate tax at a lower threshold, when preserving both spouses’ GST exemptions for grandchildren matters, when the surviving spouse faces creditor risk or the possibility of remarriage, or when sheltering decades of future growth is worth giving up the second step-up in basis.
For couples whose combined estate is comfortably under $30 million, who live in a state with no estate tax, and who plan to leave everything to the same beneficiaries, portability is often the simpler and cheaper choice. Run both sets of numbers before the first death. Once the trust becomes irrevocable, unwinding it without tax consequences is rarely possible.