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The Unlimited Marital Deduction

A powerful estate planning tool that allows spouses to transfer unlimited assets to each other free of federal estate and gift tax — and how to use it most effectively.

What Is the Unlimited Marital Deduction?

Definition

The unlimited marital deduction is a provision in the United States Internal Revenue Code that allows an individual to transfer — free from estate and gift tax — an unrestricted amount of assets to their spouse, either during life or at death.

When developing an estate plan, it is important to consider the tax impact on loved ones. The unlimited marital deduction is one of the most significant tools available to married couples for reducing or deferring federal estate tax. There is no cap on the amount that can be transferred: a spouse can leave their entire estate to the surviving spouse without incurring federal estate tax.

However, simply leaving all wealth to the surviving spouse may result in a larger-than-necessary taxable estate when the surviving spouse dies. Coordinating the marital deduction with each spouse’s lifetime federal gift and estate tax exemption is typically a more efficient approach.

Two Approaches for Married Couples

When the first spouse dies, the surviving spouse and their advisors generally choose between two strategies for handling the estate tax exemption:

Option 1

The Portability Rule

If the first spouse to die leaves less than the full applicable exemption amount to heirs other than the surviving spouse, the executor of the deceased’s estate can elect to transfer the unused portion of the exemption to the surviving spouse.

This is called portability. It effectively gives the surviving spouse access to both exemptions, potentially shielding up to $27.98 million (2025) from federal estate tax.

Key limitation: Portability generally does not apply to state estate tax exemptions or the federal generation-skipping transfer tax exemption. Unused state exemptions and GST exemptions of the first spouse to die will be lost without trust planning.

Option 2

The Two-Trust Strategy

An alternative to portability is to use an exemption trust (also called a bypass trust or credit shelter trust) combined with a marital trust. This approach splits the estate at the first death into two components, each serving a distinct purpose.

This strategy can be more flexible and tax-efficient than portability in certain situations — particularly where state estate taxes apply, where GST planning is needed, or where asset protection and inheritance control are priorities.

The Two-Trust Strategy Explained

In a two-trust approach, the first spouse’s estate is divided into two components at death. Here is how the split works using a 2025 example:

Two-Trust Strategy — 2025 Example ($14 Million Estate)
First Spouse’s Estate: $14,000,000
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Exemption Trust Bypass Trust / Credit Shelter Trust $13,990,000 Funded up to the federal lifetime exemption. Shielded from estate tax now and at surviving spouse’s death.
Marital Trust QTIP or Outright to Spouse $10,000 Remaining assets pass to surviving spouse under the unlimited marital deduction. No estate tax at first death.

The result: no federal estate tax at the first spouse’s death. Assets in the exemption trust are offset by the federal estate tax exemption; assets in the marital trust are shielded by the unlimited marital deduction.

The Two Trusts in Detail

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Exemption Trust

Also called: Bypass Trust, Credit Shelter Trust (CST), Family Trust

The exemption trust is designed to prevent estate taxation on its assets when the surviving spouse eventually dies. Assets placed in the exemption trust are offset by the deceased spouse’s federal lifetime gift and estate tax exemption at the first death — meaning no estate tax is owed at that point.

Critically, these assets also escape estate tax at the surviving spouse’s death, regardless of how much those assets may have grown in value since the first spouse died. This growth potential is one of the most powerful advantages of the exemption trust over the portability rule.

While alive, the surviving spouse has limited control over the exemption trust and limited access to its principal. Key rules:

  • The surviving spouse does not have to be a beneficiary — though they often are listed as one
  • Beneficiaries can receive income annually, or at the trustee’s discretion
  • The surviving spouse’s access to principal must be limited to prevent those assets from being included in their estate
  • Principal can be distributed at the trustee’s discretion for health, education, maintenance, or support — provided the trustee is someone other than the spouse
  • The surviving spouse may be able to designate where the balance passes, within a limited class of beneficiaries

The overriding objective is to limit the surviving spouse’s control over trust assets, so those assets escape estate taxation at the surviving spouse’s death.

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Marital Trust

Also called: QTIP Trust (Qualified Terminable Interest Property Trust)

The marital trust holds assets that pass to the surviving spouse under the unlimited marital deduction — meaning no estate tax is owed at the first spouse’s death on these assets. In most cases, the marital trust is required to distribute all income generated by its assets to the surviving spouse at least annually.

The marital trust does not provide additional tax benefits beyond the marital deduction itself. However, it offers two important non-tax advantages:

  • Inheritance control: It allows the deceased spouse to provide for the surviving spouse while directing who inherits the remaining assets after the surviving spouse’s death. This can ensure assets eventually pass to the couple’s children even if the surviving spouse remarries.
  • Creditor protection: A marital trust generally protects its assets from creditors’ claims during the surviving spouse’s lifetime.

Upon the surviving spouse’s death, assets remaining in the marital trust may be subject to estate tax (unlike the exemption trust). However, this exposure is typically reduced by the surviving spouse’s own remaining exemption.

The best-known form of marital trust is the QTIP trust (Qualified Terminable Interest Property trust), which gives the deceased spouse control over the ultimate disposition of trust assets while still qualifying for the unlimited marital deduction.

Tax Outcomes of the Two-Trust Strategy

At First Death No federal estate tax. Assets in the exemption trust are offset by the deceased spouse’s federal exemption; assets in the marital trust are shielded by the unlimited marital deduction.
At Surviving Spouse’s Death Exemption trust assets pass estate-tax-free regardless of how much they have grown. Marital trust assets may be subject to estate tax, offset by the surviving spouse’s own remaining exemption.
State Estate Taxes — Important Portability is generally not permitted for state estate tax exemptions (in states that levy state estate tax) or the federal generation-skipping transfer tax (GST) exemption. Without a credit shelter trust, any unused state estate tax exemption and GST exemption of the first spouse to die will be lost permanently. The two-trust strategy preserves both.

Estate planning requires professional coordination. The unlimited marital deduction and trust strategies involve complex tax law that changes frequently. State tax rules vary significantly. Always work with a licensed estate attorney and tax advisor for your specific situation. A fiduciary financial advisor can help coordinate the financial planning dimension before and alongside legal planning. Contact us for a free, no-obligation consultation.

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