Foreign Grantor Trust Form 3520 Tax Calculator 2026
Calculate throwback tax on foreign trust distributions, Form 3520 and 3520-A penalties, accrued interest, and compare the default method vs DNI method for US beneficiaries of foreign trusts.
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Years during which income was accumulated in the trust (not distributed)
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Assumed top rate applied each accumulation year (37% for 2026) Throwback Tax Calculation
Penalty Exposure
How Foreign Trust Throwback Taxation Works
When a foreign non-grantor trust accumulates income and later distributes it to a US beneficiary, the IRS applies the throwback rule (IRC Β§665-668). The distribution is "thrown back" to the accumulation years and taxed as if received in those years, plus an interest charge.
Default Method Throwback Tax = Distribution Γ Top Marginal Rate
Interest on Throwback = Throwback Tax Γ IRS interest rate Γ (accumulation years / 2)
Total Cost = Throwback Tax + Interest
Form 3520 Penalty = max($10,000, Distribution Γ 35%)
Form 3520-A Penalty = max($10,000, Trust Value Γ 5%)
Total Penalty = Form 3520 + Form 3520-A penalties (if applicable)
Interest on Throwback = Throwback Tax Γ IRS interest rate Γ (accumulation years / 2)
Total Cost = Throwback Tax + Interest
Form 3520 Penalty = max($10,000, Distribution Γ 35%)
Form 3520-A Penalty = max($10,000, Trust Value Γ 5%)
Total Penalty = Form 3520 + Form 3520-A penalties (if applicable)
Example β $500K distribution, 10-year accumulation, 37% top rate:
Default method throwback tax: $500,000 Γ 37% = $185,000
Interest (est. 8% Γ 5 avg. years): $185,000 Γ 8% Γ 5 = $74,000
Total throwback cost: $259,000 (52% effective rate)
Form 3520 late penalty: max($10,000, $500,000 Γ 35%) = $175,000
Combined exposure: $259,000 + $175,000 = $434,000
Default method throwback tax: $500,000 Γ 37% = $185,000
Interest (est. 8% Γ 5 avg. years): $185,000 Γ 8% Γ 5 = $74,000
Total throwback cost: $259,000 (52% effective rate)
Form 3520 late penalty: max($10,000, $500,000 Γ 35%) = $175,000
Combined exposure: $259,000 + $175,000 = $434,000
Sources & References (click to expand)
- IRC Β§6048 β Information With Respect to Certain Foreign Trusts (Form 3520/3520-A filing requirements)
- IRC Β§6677 β Failure to File Information With Respect to Certain Foreign Trusts (penalty provisions)
- IRS Form 3520 Instructions β Annual Return to Report Transactions with Foreign Trusts
- IRS Publication 519 β US Tax Guide for Aliens (foreign trust and throwback rules)
- IRC Β§665-668 β Throwback Rule for Trust Distributions (accumulation distribution treatment)
Extended
Default vs DNI Method Comparison Calculator
Toggle between default and DNI methods. Model multi-year accumulation with SVG throwback growth chart and penalty timeline.
Compare the Default Method vs DNI Method and see the difference. Model multi-year accumulation periods with interest charge growth.
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Federal short-term rate + 3% (check current IRS rate) %
Actual blended tax rate during accumulation years (often lower) Throwback Tax + Interest by Accumulation Period
Default Method Total DNI Method Total
Penalty Exposure by Years Late
| Months Late | Form 3520 Penalty | Form 3520-A Penalty | Combined Penalty | Total Cost (Default) |
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Frequently Asked Questions
What is the throwback rule for foreign trust distributions?
The throwback rule (IRC Β§665-668) applies when a foreign non-grantor trust accumulates income and later distributes it to US beneficiaries. The distribution is treated as if it were received ratably over the accumulation years. Tax is calculated at the top marginal rate that applied in each accumulation year, plus an interest charge running from the middle of each accumulation year to the date of distribution. The result: you effectively pay taxes plus interest as if you had received the income in those earlier years, which is typically far more expensive than if the trust had simply distributed income annually.
What penalties apply for not filing Form 3520 or 3520-A?
Form 3520 (US person receiving distributions from or making transfers to a foreign trust) has penalties of the greater of $10,000 or 35% of the reportable amount. Form 3520-A (annual information return of a foreign trust) has penalties of the greater of $10,000 or 5% of the gross value of trust assets. Both penalties apply separately and can stack. The IRS has increased enforcement of these filing requirements significantly, and courts have generally upheld these substantial penalties.
What is the "default method" for throwback rule calculation?
If the trust cannot provide adequate records of the accumulation period (which is common for many foreign trusts with poor recordkeeping), the IRS uses the "default method" under Temp. Reg. Β§1.665(c)-1A. The default method assumes all accumulated income was accumulated in the current year, which eliminates any opportunity to offset against losses in prior years and applies the highest current-year rate. This is almost always the worst possible tax outcome and underscores why maintaining proper trust records is critical.
Who is considered a US person for Form 3520 purposes?
A US person includes US citizens anywhere in the world, US residents (including green card holders and those meeting the substantial presence test), US corporations, partnerships, and trusts. The filing requirement applies even if you are a beneficiary and did not request the distribution. If a foreign trust makes a distribution to you in 2026, you must file Form 3520 by April 15, 2027 (or by October 15 with extension). Both the amount and the date of the distribution matter for penalty calculations.
How does the DNI method reduce throwback taxes compared to the default method?
Under the Distributable Net Income (DNI) method, you calculate the actual income accumulated in each year using the trust's books and records. This allows you to: (1) use actual tax rates from those years (which may have been lower); (2) account for losses in certain years that offset income in others; (3) calculate the interest charge precisely from the middle of each year. The DNI method requires thorough trust records β if records are unavailable, you are forced to use the harsh default method. The difference can be hundreds of thousands of dollars in accumulated cases.