TL;DR
If your living trust was written in the 1990s or 2000s, it may contain an A-B split, also called a bypass or credit shelter trust. It was designed to reduce or avoid estate tax back when the exemption was far lower. Most estates today are well under the federal estate tax exemption, so for many couples the split no longer does the job it was built for, while still costing the surviving spouse control and the children a second step-up in basis. Some families genuinely still benefit from it. Which group you are in depends on your trust and your assets, and the time to find out is while both spouses are living.
Somewhere in your trust, there is probably a paragraph you have never read that decides what happens the day one of you dies.
In many trusts written twenty or thirty years ago, that paragraph says the trust must be divided in two.
Most couples have no idea it is there. It was a sensible piece of drafting when it was written. The question worth asking now is whether it still earns its place.
On this page:
- What an A-B trust is and why yours might have one
- Why an older A-B split may no longer serve its purpose
- What the A-B split costs the surviving spouse
- Who still benefits from an A-B trust
- How to find out which group you are in
- What updating actually involves
What is an A-B trust, and why might mine have one?
An A-B trust, also called a bypass trust or credit shelter trust, is a living trust that divides into two separate trusts when the first spouse dies. One side, usually called the survivor’s trust, stays with the surviving spouse. The other, the bypass trust, holds the deceased spouse’s share and generally becomes irrevocable.
The reason for the design was estate tax. When your trust was drafted, the amount an estate could pass before any federal estate tax applied was a small fraction of what it is today, and many families were at risk of owing it. Splitting the trust at the first death was how planners helped families reduce or avoid that tax.
If your trust was written in that era, this structure was not a mistake. It was competent planning for the law as it stood.
Why might an older A-B split no longer serve its purpose?
The amount you can pass free of federal estate tax has changed dramatically.
Most estates today are well under the federal estate tax exemption. For many couples, the tax the A-B split was designed to avoid is not a concern anymore.
The split, however, is still written into the document. If your trust requires it, it will still happen unless the trust is updated.
That leaves the surviving spouse dividing the trust and running two instead of one, and it can leave your children a capital gains problem later. The structure is doing all of that to solve a tax problem most families no longer have.
What does the A-B split cost the surviving spouse?
This is the part worth picturing, because it does not land on both of you. It lands on whichever one of you outlives the other.
- Two trusts to run instead of one, with separate accounts and a separate tax return every year.
- Less freedom with money that used to be simply theirs. The bypass side is still there for the surviving spouse, but the trust sets rules about how it can be used, and those rules were locked in at the first death.
- Answering to the children about money. Whatever is left in the bypass trust generally goes to the children, which can leave the surviving spouse accountable to their own kids for how it is invested and spent.
- A tax bill waiting for your children. Assets in the bypass trust generally sit outside the surviving spouse’s estate, so they often do not get a second step-up in basis at the second death. Growth over those years can remain taxable when your children later sell the asset.
None of that is theoretical. Those are real burdens a surviving spouse may end up carrying, from a structure built for a tax most families no longer owe.
Does anyone still need an A-B trust?
Yes, and this is where a blanket answer would be wrong.
The split can still do real work for some families, and it may still make sense when:
- The estate is large enough that federal estate tax is genuinely in play, or may be by the time both spouses are gone.
- There are children from a previous marriage. Locking in where the first spouse’s share ultimately goes is often the entire point, and it has nothing to do with taxes.
- The couple wants certainty about the remainder. A bypass trust generally fixes who receives what is left, rather than leaving it to whatever the survivor decides years later.
- Creditor or remarriage protection matters to the family. That protection does not depend on the tax law, so for those couples the structure still has a job to do.
So the question is not “are A-B trusts outdated.” It is whether yours is doing something you still want done.
How do we find out which group we are in?
Someone has to read the trust. There is no way around that, and you cannot tell from the cover page or from what you remember signing.
What we look at is a short list: whether the division is mandatory or discretionary, what the bypass side would hold, what the surviving spouse would be allowed to do with it, where the remainder goes, and what your assets and their growth would actually mean for your children’s tax picture. That is a conversation, not a research project.
The thing to know about timing is that your options are much wider while both of you are living. A trust can generally be restated by the two of you together, privately, as part of an ordinary update. After the first death, the bypass side typically becomes irrevocable, and changing it can require a petition in probate court, which is a real process with real cost.
That is why this conversation is best had while both spouses are living.
What does updating actually involve?
Updating an older trust usually involves less than people expect.
When an A-B structure no longer fits, the fix is generally an amendment and complete restatement as part of an estate planning update: we rewrite the trust on a current foundation while keeping its original name and date, so your accounts and property usually do not need to be retitled. Your will, powers of attorney, and health care directive get refreshed at the same time so everything works as one set.
And if the review shows the split still serves your family, that is a real answer too. You will know why it is there, what it will require of whoever survives, and that it is a choice you are making rather than one made for you in 1998.
Either way, you stop wondering.
If your trust is more than ten years old and no one has explained whether it contains an A-B split, it is worth finding out while both of you can still make the choice together.
Schedule an Initial Planning Session or call (949) 718-0420. We will show you what your trust requires, whether the split still serves your family, and what to do next.
Laura Meier, Esq., Founder, Meier Law Firm · Newport Beach, California · Last reviewed August 2026
Frequently Asked Questions
An A-B trust, also called a bypass or credit shelter trust, is a living trust that divides into two separate trusts when the first spouse dies. One side stays with the surviving spouse. The other holds the deceased spouse's share and generally becomes irrevocable. The design was built to reduce or avoid federal estate tax back when the exemption was far lower than it is today.
For many families the tax reason behind them has largely gone, because most estates today are well under the federal estate tax exemption. That does not make the structure useless. It can still make sense for larger estates, for blended families, and for couples who want certainty about where the first spouse's share ultimately goes. Whether yours still earns its place depends on your trust and your assets.
The surviving spouse ends up running two trusts instead of one, with separate accounts and a separate tax return. Their access to the bypass side is often limited by rules the trust locked in at the first death. And because those assets generally sit outside the survivor's estate, they often do not receive a second step-up in basis, which can leave the children a capital gains bill a current plan may have avoided.
Families whose estates are large enough that federal estate tax is genuinely in play, couples with children from a previous marriage who want the first spouse's share locked to those children, and couples who want certainty about who receives the remainder rather than leaving it to the survivor's later decisions. For some families, creditor or remarriage protection is another reason the structure may still serve an important purpose.
While both spouses are living, usually yes. The trust can generally be restated on a current foundation as part of an ordinary update, keeping its original name and date so accounts usually do not need retitling. After the first death the bypass side typically becomes irrevocable, and changing it can require a petition in probate court. That difference is why this is worth handling while you both can.
You generally cannot tell from memory or from the first page. It takes reading the document to see whether a division is required at the first death, whether it is mandatory or discretionary, what the bypass side would hold, and what the surviving spouse could do with it. If your trust is more than ten years old and no one has ever raised this with you, it is worth checking.
It can. Assets in the bypass trust generally sit outside the surviving spouse's estate, so they often do not receive a second step-up in basis at the second death. Growth over the years between the two deaths can remain taxable to the children when they sell. Assets in the survivor's trust are treated differently and generally do receive that adjustment.
Usually an amendment and complete restatement. The trust is rewritten on a current foundation while keeping its original name and date, so your accounts and property generally do not need to be retitled. The will, powers of attorney, and health care directive are refreshed at the same time so the plan works as one set. Most families complete an update in about four to five weeks.
When you are ready, we are here.
One conversation, at whatever pace your family needs. We will help you understand which path you are on, what the deadlines are, and what does not need to be rushed.
Talk with us when you are ready
Or call (949) 718-0420