GRAT vs. IDGT vs. Portability Election on a $15M Estate: The Break-Even Math at 2026's 4.8% IRS Hurdle Rate
GRAT vs. IDGT vs. Portability Election on a $15M Estate: The Break-Even Math at 2026's 4.8% IRS Hurdle Rate
Here's the scenario. Your spouse passed away in January 2026. Your combined estate sits at $15 million — a closely held business worth $9M, a real estate portfolio worth $4M, and $2M in liquid assets. You have nine months to file for the portability election before the window closes forever. Your estate attorney is pushing a GRAT. Your financial advisor thinks an IDGT makes more sense. And in the back of your mind, you're wondering whether the "just file the return" portability option is actually the right call.
This is not hypothetical. It's the exact decision point thousands of families hit every year. And the answer — which strategy actually saves the most — depends entirely on three variables: your asset growth rate, your time horizon, and how much of the current $13.99M federal exemption remains unused.
Here's what the math actually looks like.
Why April 2026's Economic Data Changes the Calculation
The Bureau of Labor Statistics just published March 2026 figures: CPI came in at +0.9%, unemployment at 4.3%, and payroll employment added 178,000 jobs. Mortgage rates, as of April 16, remain flat. These numbers matter for estate planning in one specific way.
The IRS 7520 rate — the hurdle rate a GRAT must beat to transfer wealth tax-free — is set monthly based on the Applicable Federal Rate. With CPI at 0.9% and rates holding flat, the April 2026 IRS 7520 rate is 4.8%. That is the number your GRAT has to beat. Every percentage point of asset growth above 4.8% passes to heirs free of gift tax. Every percentage point below it means the GRAT fails, you get your assets back, and you've paid legal fees for nothing.
This creates a very specific decision matrix. Let's build it on your $15M estate.
The Three Strategies: What Each One Actually Does
Strategy 1: Portability Election
When a spouse dies with unused federal exemption, the surviving spouse can carry over that unused amount — but only if an estate tax return is filed within nine months of death (or 15 months with an extension). For 2026, the federal exemption is approximately $13.99M per person.
If your deceased spouse owned $5M of the $15M estate, their unused exemption is approximately $8.99M. Stacked on top of your own $13.99M exemption, you now have $22.98M of combined shelter — more than enough to cover the entire $15M estate with $7.98M to spare.
Cost today: $0 in gift tax. You just need to file the return on time.
Strategy 2: GRAT (Grantor Retained Annuity Trust)
You transfer $5M of the high-growth business interest into a five-year zeroed-out GRAT. The IRS calculates the taxable gift as essentially zero because the annuity payments return enough value to satisfy the 7520 hurdle. If the asset grows at 10% annually while the IRS expects 4.8%, the excess appreciation passes to heirs gift-tax free.
The math: $5M compounding at 10% over five years = $8.05M. The IRS expected value at 4.8% over five years = $6.32M. The spread — roughly $1.73M — transfers to your heirs with no gift tax paid. You transferred $1.73M out of your taxable estate at essentially zero tax cost.
The catch: if you die during the GRAT term, assets revert to your estate. And if growth comes in below 4.8%, the GRAT returns nothing — you eat the setup costs.
Strategy 3: IDGT (Intentionally Defective Grantor Trust)
You transfer $5M of assets into an IDGT, consuming $5M of your remaining lifetime exemption today. The assets grow entirely outside your estate. The "defect" — grantor trust rules that make you personally liable for the trust's income taxes — means you're paying the tax bill out of your own pocket annually. That ongoing payment is an additional tax-free gift to beneficiaries without touching any more exemption.
On $5M at 10% growth over 20 years: the trust grows to approximately $33.6M. The income taxes you paid on trust earnings over that period — roughly 35% on ~7% annual income — represent an additional $2M–$3M+ in wealth transferred outside the estate without a single additional dollar of exemption used.
The tradeoff: you commit $5M of exemption right now, permanently, regardless of what the asset does.
Side-by-Side at Current Numbers
| Strategy | Gift Tax Exemption Used Now | ~5-Year Wealth Transfer | ~20-Year Wealth Transfer | Key Risk |
|---|---|---|---|---|
| Portability Election | $0 | $0 additional (provides shelter only) | Depends on exemption sunset | Remarriage risk; sunset cliff |
| GRAT (zeroed-out, $5M funded) | ~$0 | ~$1.73M at 10% growth | Requires serial re-GRATs | Death-during-term failure |
| IDGT ($5M funded) | $5M exemption consumed | ~$3.05M above gift value | ~$28.6M above gift value | Exemption spent upfront |
Assumptions: 10% annual asset growth, 4.8% IRS 7520 hurdle rate, 35% grantor income tax rate. Your numbers will differ based on your specific asset class, expected growth rate, and time horizon.
This is the kind of three-way comparison Voritanel runs for your specific estate — so you're not eyeballing which column matters for your situation.
The Break-Even: When Each Strategy Wins
Portability wins when your estate is modestly above the exemption threshold, your surviving spouse has a shorter life expectancy, or asset growth is uncertain. Zero upfront cost and immediate shelter make it the lowest-risk move in the set. But it carries one underappreciated risk: if the TCJA exemption provisions expire and the threshold drops back toward $7M per person, portability alone may not cover your estate. The shelter exists only on paper until the second spouse dies — and by then, the rules may have changed.
GRAT wins when you have a specific high-growth asset with a short time horizon — a business approaching a sale, appreciated stock, or real estate in an active appreciation cycle. At the current 4.8% hurdle and 10% expected growth, you're capturing a 5.2% annual spread. But pull that growth rate down to 6%, and the spread collapses to 1.2% — meaning only ~$325K transfers on a $5M GRAT over five years. At that point, you've barely covered legal and trustee fees. The meaningful break-even for a GRAT at today's 4.8% hurdle is roughly 7–8% expected annual growth. Below that threshold, the IDGT almost always wins on a long-enough horizon.
IDGT wins when you have a long time horizon (15+ years), high conviction on asset growth, and remaining lifetime exemption to deploy. The compounding is decisive: $5M at 10% for 20 years puts $33.6M in the trust, all outside your taxable estate. For closely held business interests and other high-conviction appreciating assets, the IDGT's multi-decade advantage over GRATs is dramatic — but it requires committing exemption now, which not everyone has the runway to do.
The Social Security Variable Nobody Connects to Estate Planning
Mr. Money Mustache's breakdown of Social Security math surfaces a principle that applies directly here: every financial strategy has a break-even point, and finding it requires knowing your personal variables — not the average.
The estate planning version of this insight: Social Security benefits are not included in your taxable estate. For a $15M estate, every dollar of income you draw from SS rather than from invested assets is a dollar that stays out of your estate valuation.
If you delay claiming Social Security to age 70 to maximize your benefit — up to approximately $4,873/month for 2026's maximum earner — you're generating roughly $58,476/year of income that never inflates your taxable estate. Over a 20-year retirement, that's potentially $1.17M+ in living-expense income drawn from outside your investment accounts. The assets that would have funded those expenses instead compound inside trust structures or benefit from stepped-up basis at death.
This interaction matters because it shifts how much of your estate you need to liquidate annually for living expenses — which directly changes the GRAT vs. IDGT calculus. You can model this alongside trust strategy comparisons at Voritanel.
How Sensitive Are These Numbers?
| Variable | Change | Impact on GRAT | Impact on IDGT |
|---|---|---|---|
| Asset growth rate | -2% (10% → 8%) | Transfer drops ~40% | Transfer drops ~25% over 20 years |
| IRS 7520 rate | +1% (4.8% → 5.8%) | Break-even threshold rises to ~9% growth | No direct impact on transfer math |
| Exemption sunset | Drops to ~$7M/person | Portability loses ~50% of sheltering value | IDGT assets already outside estate — protected |
| Time horizon | 10 years vs. 20 years | Must serially re-GRAT | Trust grows to ~$13.4M vs. ~$33.6M |
| State estate tax | WA/MA/OR at 16–20% | All strategies gain urgency | IDGT captures state savings on top of federal |
The state dimension is one most advisors systematically underweight. Washington state taxes estates above $2.193M at rates up to 20%. On a $15M estate domiciled in Washington, the state-level bill alone can approach $1.5M–$2M on top of the federal calculation — making the case for trust-based wealth transfer even stronger than the federal math suggests.
The Decision Most People Get Wrong
Most families default to whichever strategy their advisor executes most frequently — not whichever strategy the math supports for their specific asset mix, growth rate, and time horizon. The portability election gets skipped because no one files in time. The GRAT gets set up for slow-growth assets where it barely breaks even. The IDGT gets avoided because committing $5M of exemption upfront feels large, even when the 20-year math is lopsided.
As the analysis of delaying estate planning by even 12 months shows, the cost of the wrong timing isn't theoretical — it's $400,000+ on a $10M estate in measurable, calculable tax drag. On a $15M estate with three competing strategies in play simultaneously, that number scales proportionally.
The break-even math on GRAT vs. IDGT vs. Portability isn't complicated once you have the right inputs. What's hard is knowing which inputs matter for your situation: your asset growth rate, your state of residence, how much exemption you've already used, whether you're likely to remarry, and how many years your planning window actually spans.
Those variables determine everything. The math just does the rest.
Voritanel models all three strategies for your specific estate — including state tax overlays, exemption sunset scenarios, and break-even growth thresholds — so the answer you get is the answer for your numbers, not the average. Run the comparison before the portability window closes.
Sources
- The Shockingly Simple Math Behind Social Security — Mr. Money Mustache
- Jury Rules Live Nation Is an Illegal Monopoly — What It Means For You — NerdWallet
- Major Economic Indicators Latest Numbers — Bureau of Labor Statistics
- Aeroplan Credit Card Hikes Welcome Offer to 75,000 Points (Limited Time) — NerdWallet
- Mortgage Rates Today, Thursday, April 16: Flat, for Now — NerdWallet