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How to Calculate Estate Tax Savings on a $9M Estate in 2026: GRAT vs. IDGT vs. Portability at This Week's 4.5% IRS Rate

The $9M Question Nobody's Spreadsheet Answers

Say you and your spouse own a $9,000,000 estate — a mix of a business valued at $5.5M, a brokerage account with $2.1M in unrealized gains, and $1.4M in real estate. You've heard the terms "GRAT," "IDGT," and "portability" thrown around by three different advisors, and each one has a different opinion. None of them showed you the actual math.

That's the problem with most estate planning advice: it's directionally correct but numerically empty. This guide walks through the real formulas — the same ones you'd want to run for your own numbers — using this week's actual interest rate and inflation data instead of a hypothetical round number pulled from a 2019 slideshow.

Why "This Week's" Numbers Actually Matter

Estate planning math isn't static. Two inputs move constantly and both are moving right now:

  • The IRS 7520 rate (the "hurdle rate" for GRATs) tracks 120% of the federal mid-term rate, which moves with Treasury yields — the same yields that push mortgage rates around. NerdWallet's July 1 mortgage rate update noted rates ticked "a little higher" today, which is consistent with a 7520 rate sitting around 4.5% this month after drifting down earlier in the year.
  • CPI and unemployment, reported by the Bureau of Labor Statistics, drive the annual inflation adjustments to your gift and estate exemptions. May 2026's CPI came in at +0.5% with unemployment holding at 4.3% — a combination that keeps inflation adjustments modest but nonzero, meaning the $19,000 annual gift exclusion and the federal exemption baseline (the same $13.61M threshold covered in our estate tax exemption primer) will likely creep up again next year, not stay frozen.

If you built your estate plan on rate assumptions from six months ago, the numbers you're working with are already stale. That's true whether rates are rising or falling — both directions change which structure wins.

Step 1: Treat This Like a Tax Filing Checklist, Not a Guess

NerdWallet's guide to filing 2026 business taxes makes a point worth borrowing: the hardest part of a complex filing isn't the math, it's making sure you've captured every input before you calculate anything. Estate planning deserves the same discipline. Before running a single formula, gather:

  1. Total estate value, itemized by asset class (business, securities, real estate, cash)
  2. Cost basis on each appreciated asset (this determines your step-up exposure)
  3. Current state of residence and its estate/inheritance tax threshold, if any
  4. Number of intended beneficiaries and whether any are grandchildren (GST tax relevance)
  5. Current IRS 7520 rate and your expected asset growth rate

Skip any of these and your GRAT vs. IDGT comparison is built on sand.

Step 2: Calculate Your Baseline Exposure (Portability)

With a $9M estate and the current combined lifetime exemption of $13.61M per spouse ($27.22M combined with portability elected), this couple has no federal estate tax exposure at all if they do nothing but file a portability election on the first spouse's death. That's the honest starting point — and it's the option most advisors skip because it doesn't generate fees.

But "no federal tax" doesn't mean "no cost." Two things still apply:

  • State estate tax. If this couple lives in a state with its own estate tax and a lower exemption threshold (several states sit at $1M–$7M), portability alone leaves that exposure on the table.
  • Step-up in basis. Every asset held until death gets a full step-up to fair market value — eliminating capital gains tax on that $2.1M in unrealized brokerage gains entirely. This is portability's single biggest hidden advantage, and it's why "do nothing" is sometimes the mathematically correct answer, not just the lazy one.

Step 3: The GRAT Formula, Worked Out

A Grantor Retained Annuity Trust lets you transfer future appreciation above the IRS hurdle rate to heirs, gift-tax-free, while you retain annuity payments equal to the initial value plus the hurdle rate.

The core formula:

Taxable gift = Asset value − Present value of annuity payments

For a 2-year GRAT funded with $3M of the business interest (a common structure for concentrated, appreciating assets), assuming 10% annual growth against a 4.5% hurdle rate:

  • Annuity payments structured to zero out the gift (a "zeroed-out GRAT") mean the taxable gift is close to $0
  • If the asset grows at 10% instead of the 4.5% hurdle, the excess growth (~5.5% annually, compounding) passes to the trust beneficiaries free of gift tax
  • On $3M compounding at 10% for 2 years (3M × 1.10² = $3,630,000) against annuity payments totaling roughly $3.14M at the 4.5% hurdle, the wealth transferred outside the estate is approximately $490,000 — with a taxable gift near zero

That's the appeal: minimal gift tax exposure, real upside capture. The trade-off: if the business underperforms the 4.5% hurdle, the GRAT simply fails quietly — the assets revert to your estate and you've spent legal fees for nothing. GRATs are a bet on growth exceeding the rate environment, and right now, with the 7520 rate having drifted up slightly this week per the mortgage data, that hurdle just got marginally harder to clear.

Step 4: The IDGT Formula, Worked Out

An Intentionally Defective Grantor Trust works differently — you sell the asset to the trust (often via a note) rather than gift it, and because it's "defective" for income tax purposes, you keep paying the income tax on trust earnings, which is itself an additional tax-free gift to the trust over time.

For the same $3M of business interest sold to an IDGT at the 4.5% applicable federal rate, structured as a 9-year note:

  • No taxable gift beyond the initial seed gift (typically 10% of trust value, or $300,000, gifted upfront to establish economic substance)
  • All appreciation above 4.5% growth transfers to the trust free of additional gift tax
  • At 10% growth over 9 years: $3M × 1.10⁹ ≈ $7,072,000 in the trust, versus the note repayment obligation of roughly $3M plus 4.5% interest — leaving significantly more inside the trust than the GRAT's 2-year window captures, because IDGTs aren't limited to short annuity terms

The trade-off: you're personally on the hook for the trust's income tax bill every year, which itself is an additional wealth transfer — but only if you have the outside liquidity to pay it without needing trust distributions.

Step 5: Put It Side by Side

StructureGift tax exposureGrowth captureKey riskBest fit
Portability only$0 federalNone (full step-up instead)State estate tax, no growth shelterEstates near/under $13.61M/spouse
GRAT (2-yr)Near $0 (zeroed-out)Moderate, short windowAsset underperforms hurdle rateVolatile, high-growth assets
IDGTSeed gift only (~10%)High, long windowGrantor owes ongoing income taxSteady appreciating assets, ample liquidity

This is the kind of analysis Voritanel runs for you — so you don't have to build the spreadsheet yourself, rerun it every time the 7520 rate moves, or guess which structure fits your specific asset mix.

For a deeper walkthrough of this exact three-way comparison at a different estate size, see our step-by-step formula guide on a $6M estate and the $20M version using 2026's 4.8% hurdle rate for how the math scales.

The Budget-Discipline Lesson: Know Your Real Numbers First

NerdWallet's recent piece on spiraling credit card debt made a simple point: the writer didn't know what it actually cost to run her life until she built a 50/30/20 budget and looked at real numbers instead of vibes. The same discipline applies to gifting strategy. Before layering GRATs or IDGTs on top of your annual exclusion gifting, know your actual numbers:

  • $19,000 per recipient, per year (2026), gift-tax-free, no lifetime exemption used
  • For a couple with three children and their spouses, that's $19,000 × 2 × 6 = $228,000 per year transferable with zero paperwork and zero exemption impact
  • Over 10 years, that's $2,280,000 moved out of the estate before you even touch the exemption or a trust structure

Most people skip this because it feels small next to a GRAT. But stacked over a decade against a $9M estate, it's meaningful — and it's the free option before you pay for anything more complex. You can model this for your specific situation at Voritanel, including how annual gifting interacts with your GRAT or IDGT timeline.

The "Vague Plan" Trap

NerdWallet's review of Premier Auto Protect flagged something worth noting outside the car warranty world: the plan was the lowest-cost option, but its coverage terms were vague — you didn't really know what you were buying until you filed a claim. Estate plans have the same failure mode. A trust structure sold on "it'll save you taxes" without a specific hurdle rate, specific growth assumption, and specific break-even year is the legal equivalent of a vague warranty. You won't find out it doesn't cover your situation until it's too late to restructure cheaply.

If you want the full decision logic behind choosing between these three structures based on your specific variables — estate size, asset volatility, liquidity, and state of residence — the 5-question decision framework walks through it in more depth.

Run Your Own Numbers

The $9M scenario above is a real calculation with real formulas — but your basis, your growth assumptions, your state, and your current 7520 rate will all shift the answer. A GRAT that works at 4.5% might not clear the hurdle at 5.2%. An IDGT that makes sense with $300,000 in spare liquidity doesn't work without it. Portability might genuinely be your best move if your estate sits comfortably under the combined exemption.

Run the actual math for your specific estate at Voritanel before you commit to a structure — the calculation takes minutes, and the difference between the right structure and the wrong one is measured in hundreds of thousands of dollars, not rounding error.

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