$18M Estate, Bond Yields at 20-Year Highs: GRAT vs. IDGT vs. Waiting If the AI Boom Fades or Keeps Running
Picture a single, widowed 62-year-old with an $18 million estate. Around $6 million of it sits in a low-cost stock index fund with a heavy tilt toward the AI-driven names that have led the market. The rest is a house, a business interest, and cash. She reads the headlines this week and asks two questions:
- If the AI bubble pops, did I just wait too long to move assets out of my estate?
- If it keeps running, am I giving away growth I could have kept?
The answer changes with her numbers. What follows is a worked example, not a recommendation. Your inputs will differ, but the structure of the comparison should carry over.
What the Market Data Is Telling Us This Week
Here is what the five articles behind this post say.
- Bond yields are at 20-year highs. NerdWallet's piece on why the bond market's struggles are driving up mortgage rates says inflation, an AI borrowing boom, and rising government debt are pushing yields to their highest levels in two decades.
- Mortgage rates are still above 7%. NerdWallet's September 25 update says rates fell a little today but remain "solidly above 7%."
- Inflation is not cooling on schedule. The Bureau of Labor Statistics shows CPI up 0.4% in August 2026, unemployment at 4.1%, and payrolls up 162,000 (preliminary).
- The stock market keeps surprising people. Mr. Money Mustache's "Will the AI Bubble Destroy our Retirement?" makes the point that record highs and crashes both make people nervous, and that neither one tells you what to do.
A single 0.4% monthly CPI reading annualizes to about 4.9% (1.004¹² ≈ 1.049). One month is noisy, so treat that as a warning light, not a forecast.
Why should an estate planner care about mortgage rates? Because the same forces set the rates that drive wealth transfer math. The IRS 7520 rate, which is the "hurdle" a GRAT must beat, moves with Treasury yields. Applicable federal rates, which set the interest on an IDGT sale note, move with them too. Recent Voritanel posts have modeled the hurdle near 4.8% to 5%. Check the current month's published rate before you rely on any figure below.
The Federal Backdrop: Why $18M Matters and $10M Often Doesn't
The 2026 federal estate tax exemption is $15 million per person. The annual gift exclusion is $19,000 per recipient.
An $18M single filer is $3M over the exemption. At the 40% top rate, that is about $1.2M in federal tax today, before any growth. If you are at $10M, federal estate tax is likely zero, and your real questions are state estate tax and step-up in basis. We covered that trade-off in GRAT vs. IDGT vs. Portability on a $7 Million Estate.
The problem with "wait and see" is that growth compounds the taxable portion. If the $18M grows at 8% for 10 years, it becomes about $38.9M. That leaves roughly $23.9M over the exemption, or about $9.5M in tax at 40%. (This example ignores inflation indexing of the exemption and any future law changes, both of which move the answer.)
Scenario Table: A $4M, 2-Year Zeroed-Out GRAT Under Four Market Paths
Suppose she funds a 2-year zeroed-out GRAT with $4M of the index fund. Assume a 7520 rate of 4.8% (an assumption, not a quote). The annuity payment that zeroes out the gift is about $2,145,080 per year, or roughly $4.29M in total.
Here is what passes to heirs under four annual return paths, assuming the same return in both years:
| Annual return | Value after year 1 (after payment) | Remainder to heirs | Federal tax avoided (40%) |
|---|---|---|---|
| -15% (bubble pops) | $1.25M | $0 (GRAT fails) | $0 |
| 0% (flat) | $1.85M | $0 (GRAT fails) | $0 |
| +10% | $2.25M | about $335,000 | about $134,000 |
| +20% | $2.65M | about $1.04M | about $416,000 |
The point of the table is the asymmetry. In the two bad scenarios, the GRAT returns the assets to her, less legal and setup costs. Those are a few thousand dollars or more, depending on your attorney, and you should get a quote. In the two good scenarios, growth above the 4.8% hurdle leaves the estate.
A GRAT does not protect you from a crash. It just doesn't punish you for trying before one. For more on how term length changes this, see Why Term Length Decides Whether You Lose $32,000 or $201,000.
This is the kind of scenario grid Voritanel builds for you, so you don't have to construct the spreadsheet yourself.
The Hidden Cost: Higher Yields Cut Both Ways
Yields at 20-year highs push the hurdle up, so a GRAT must beat a higher number. Using a 4.8% hurdle instead of, say, 4.0% on the same $4M, 2-year GRAT costs about $32,000 less in remainder in the +10% scenario. That rough figure comes from the same annuity math shown above. You can check it yourself by re-running the payment formula at 4.0%.
A higher rate is not all bad news, though. It helps in other structures:
- Charitable remainder trusts get a larger charitable deduction at higher 7520 rates, which improves the math for concentrated stock. See GRAT vs. Charitable Remainder Trust on $4M in Concentrated Stock.
- Lower asset values help the transfer. When markets fall, a gift or GRAT funded at the low uses less exemption per share.
- High rates raise the cost of borrowing. An IDGT sale note pays interest at the AFR. That interest is income to the grantor but is not taxed, because the trust is a grantor trust. The note's higher rate means the trust must earn more to come out ahead.
GRAT vs. IDGT vs. Waiting: A Side-by-Side for the Same $18M Estate
Here is the same person compared across three paths. Numbers are illustrative.
| Factor | GRAT (2-year, $4M) | IDGT (sale, $4M) | Wait and hold |
|---|---|---|---|
| Hurdle | 7520 rate (assumed 4.8%) | AFR on the note | None |
| Downside if market falls | Fails, assets return | Trust bears the loss, the note is still owed | Estate shrinks, tax falls |
| Uses exemption? | Little to none (zeroed-out) | Seed gift (often about 10% of the sale) | No |
| Step-up at death? | Lost on remainder | Lost on trust assets | Kept |
| Estate tax on growth | Removed above hurdle | Removed above AFR | 40% of growth |
| Complexity and fees | Moderate | Higher | Lowest |
The step-up row is the one people skip. If she holds $4M of stock with a $1.5M basis until death, her heirs get a basis of the full date-of-death value. That wipes out the embedded gain. In a trust that removes the asset from her estate, they carry over her $1.5M basis and owe capital gains tax if they sell.
At a 20% federal long-term rate plus 3.8% net investment income tax (23.8% combined), $2.5M of built-in gain is about $595,000 of tax. That is on the same order as the estate tax the trust was meant to avoid. Whether the trade-off is worth it depends on your holding period, your state, and whether the assets are likely to be sold. We work through it in How to Calculate GRAT vs. IDGT Savings on a $17 Million Estate: The Step-Up Basis Trade-Off Formula.
The Cash Side: Bonuses, CDs, and Why a $300 Perk Isn't a Plan
NerdWallet's article on switching banks for a bonus is a reminder that cash decisions carry small dollar amounts next to the numbers above. Bonuses typically require direct deposits or a minimum balance held for some months. Their value is often a few hundred dollars, and it's usually taxable as interest income (check the terms of any specific offer). I'm not saying not to chase one. But compare it to what matters:
- A $19,000 annual exclusion gift to each of three children and their spouses removes $114,000 from the estate in one year, using no lifetime exemption.
- Growth on those assets from then on also sits outside the estate. At 8% for 10 years, $114,000 becomes about $246,000, so about $132,000 of growth is out of the estate. At 40%, that is roughly $53,000 of tax not owed.
A bank bonus and an annual gift are not competing choices. But the gap in scale shows where the attention belongs. For a fuller look, see The $19,000 Gift Tax Exclusion vs. a 4.5% CD Ladder.
Reading the AI-Bubble Question Honestly
Mr. Money Mustache's point is that you can't time this. I'd add that you don't need to for the planning question. Here is how each path looks:
If the bubble pops.
- Your estate shrinks, and so does the tax.
- A GRAT funded after a decline transfers more per dollar of exemption or hurdle-beating growth, but only if a rebound follows.
- Gifting depressed assets uses less exemption. Note that gifting loses the step-up.
If the boom keeps running.
- Growth accelerates the taxable portion. At +20% a year, the GRAT above passes about $1.04M outside the estate.
- Waiting costs more with every year of growth. The cost of a 12-month delay on a $10M estate is worth reading for the mechanics.
If it's choppy and sideways.
- GRATs tend to fail quietly, which costs you fees but not much else.
- A "rolling" series of short GRATs can capture volatility, but each one has its own setup costs.
Where Your Numbers Will Differ
Everything above is a single example. These variables can flip the answer:
- Your state. Some states tax estates below the federal exemption. Massachusetts, for example, has a much lower threshold, and there is no state portability. See the $8M Massachusetts example.
- Your basis. Low-basis stock favors holding for the step-up. High-basis assets lose little by leaving the estate.
- Your marital status. A married couple has $30M of combined exemption, and portability can preserve a deceased spouse's unused amount if the election is filed.
- Your time horizon. At 62 with a family history of longevity, ten years of compounding matters. At 85, it may not.
- Your concentration. Six million in a handful of AI names carries a different risk than the same amount spread widely.
- Your actual hurdle rate. Use this month's 7520 rate and AFR, not the one in this post.
- Your charitable intent. If a gift to charity is planned anyway, a charitable remainder trust can beat both a GRAT and holding for the step-up.
A Simple Way to Start
Before you talk to an attorney, gather five things: your current estate value, the basis of your largest holdings, your state, this month's 7520 rate, and the growth rate you'd consider plausible and pessimistic. Then run at least three cases: a crash, a flat market, and a boom. If the GRAT outcome barely changes across the three cases while the "wait" outcome swings by seven figures, that tells you something.
You can model your version of this table, with your own basis, state, and rate assumptions, at Voritanel. Rates and markets are moving fast, so it's worth seeing where you stand this week.
None of this pushes you toward a trust, a gift, or doing nothing. Sometimes the math says wait, and sometimes it doesn't. It just helps to see the numbers before you decide.
This post is educational, uses illustrative assumptions, and isn't tax or legal advice. Work with a qualified estate planning attorney before acting.
Sources
- Will the AI Bubble Destroy our Retirement? — Mr. Money Mustache
- Should I Switch to a New Bank Just to Earn a Bonus? — NerdWallet
- Major Economic Indicators Latest Numbers — Bureau of Labor Statistics
- Why the Bond Market’s Struggles Are Driving Up Mortgage Rates — NerdWallet
- Mortgage Rates Today, Friday, September 25: A Little Relief, but Still Above 7% — NerdWallet