US Estate Tax vs Spanish Inheritance Tax: How Both Hit a Cross-Border Estate (and How to Plan)
How US federal estate tax and Spanish inheritance tax (ISD) can both hit the same cross-border estate at once, why there is no estate and gift tax treaty between the two countries, where the two systems collide, and which credits, the step-up in basis and planning tools reduce or remove double taxation.
By Jacob Salama, international tax lawyer (Bar no. 11.294, Málaga)
9/22/202611 min read
Further reading — our dedicated site on international inheritance in Spain.
US Estate Tax vs Spanish Inheritance Tax: How Both Hit a Cross-Border Estate (and How to Plan)
When a family has a foot in both the United States and Spain, death does not simplify the paperwork — it multiplies it. Two completely different tax systems can reach the same estate at the same time, and because there is no estate and gift tax treaty between the two countries, nothing automatically stops them from overlapping. The result is a real risk of paying tax twice on the same assets unless the estate is planned and administered with both systems in mind.
This guide explains, in plain language, how the US federal estate tax and the Spanish Impuesto sobre Sucesiones y Donaciones (ISD) each work, why they differ so much, where they collide, and what tools reduce or eliminate double taxation. It is written for US citizens living in Spain, for Spanish residents inheriting from a US relative, and for anyone with assets on both sides of the Atlantic.
Why are US estate tax and Spanish inheritance tax so different?
The first thing to understand is that these are not two versions of the same tax. They are built on opposite philosophies.
The US federal estate tax is a tax on the estate — on the total value of everything the deceased owned at death, before anything passes to the heirs. The estate itself files a return and pays the tax; the beneficiaries receive what is left. It does not matter, for the federal calculation, whether the money goes to a spouse, a child, or a stranger (although a surviving US-citizen spouse benefits from an unlimited marital deduction). It is a tax on the transferor.
The Spanish ISD is the mirror image. It is a tax on the heir — on each beneficiary individually, based on what that specific person receives, their relationship to the deceased, and their own pre-existing wealth. Two people inheriting from the same estate can pay very different amounts. It is a tax on the recipient.
That single difference — tax on the giver versus tax on the receiver — drives almost every planning decision below.
What is the US federal estate tax threshold in 2026?
The US federal estate tax only bites above a very high exemption. As of 2026, the federal basic exclusion amount is in the region of 13.6 million dollars per individual (indexed annually for inflation), which means a married US couple can shield roughly double that with proper planning. The top federal rate above the exemption is 40%.
Because the exemption is so high, the vast majority of estates never pay any federal estate tax at all. This is a crucial point that catches Spanish advisers off guard: an American client may be genuinely wealthy and still owe zero US estate tax.
Two important caveats, stated with the caution these figures deserve. First, the exemption amount changes every year and you should always confirm the current figure at the moment of death rather than rely on a number from an old article. Second, the elevated exemption introduced by the 2017 tax reform was originally scheduled to "sunset" — to fall back to a much lower level (roughly half) after 2025. Subsequent legislation has affected that timetable, so the position for deaths in 2026 and beyond must be checked against the law actually in force at the relevant date. Do not plan on the assumption that today's high exemption is permanent.
Separately, more than a dozen US states levy their own state estate or inheritance tax with far lower thresholds. Whether a state tax applies depends on the deceased's domicile and where the property sits, and it matters for the Spanish side because, as we will see, it can generate a credit.
How does Spanish inheritance tax work by comparison?
Spanish ISD has no generous million-euro federal-style exemption. In principle it applies from the first euro inherited. What softens it dramatically is that ISD is partly a regional tax: each Spanish autonomous community can set its own reductions, allowances and — most importantly — bonificaciones (rebates) that can slash the final bill by 95% or 99% for close relatives.
So the effective cost of Spanish inheritance tax depends enormously on which region's rules apply and on the relationship between the deceased and the heir. A child inheriting in Madrid or Andalusia may pay almost nothing; the same child inheriting under the state default rules, or a distant relative or unrelated beneficiary anywhere, can face a heavy bill. The Spanish rate is progressive and, once multiplier coefficients for distant relatives and wealthy heirs are applied, the effective top rate can climb well above the headline scale.
We explain the regional differences in detail in our guide to inheritance tax in Spain for foreigners and the differences between autonomous communities.
Is there a US–Spain treaty to prevent double inheritance taxation?
No. This is the single most important fact in cross-border estate planning between these two countries. The United States and Spain have an income tax treaty, but they have no treaty covering estate, inheritance or gift tax. (People often confuse the two — the income treaty deals with pensions, dividends and Social Security, not death taxes; see our explainer on the US–Spain tax treaty and the saving clause.)
Because there is no death-tax treaty, there is no treaty mechanism to allocate taxing rights or to force one country to give way to the other. The same asset can therefore be taxed by the US estate tax and by the Spanish ISD simultaneously. Relief, if any, comes not from a treaty but from the internal rules of each country.
What relief exists without a treaty?
On the Spanish side, relief comes from the deduction for international double taxation in Article 23 of the Spanish Inheritance and Gift Tax Act (Ley 29/1987, LISD). In broad terms, a Spanish-resident heir can deduct from their ISD bill the lesser of (a) the foreign inheritance tax actually paid abroad on assets located outside Spain, or (b) the average Spanish rate applied to those same foreign assets. It is a credit designed to avoid taxing the foreign-situated portion twice, but it is capped and it only reaches foreign tax genuinely comparable to ISD.
On the US side, the estate can, in the right circumstances, claim a credit or deduction for foreign death taxes attributable to foreign-situated property, and a US state estate tax may itself be creditable or deductible. The interaction is technical and asymmetric, which is exactly why the order in which the two returns are prepared, and how each asset is characterised and situated, has to be planned deliberately.
What is step-up in basis and why does it matter across borders?
One of the most valuable — and most misunderstood — features of the US system is the step-up in basis at death. When someone dies, the cost basis of most of their assets is reset to the fair market value at the date of death. An heir who later sells inherited shares or property is taxed only on the gain after death, and decades of accumulated capital gain can effectively disappear for US income tax purposes.
Spain does not offer an equivalent step-up for its own capital gains tax. For Spanish IRPF purposes, the heir generally takes as their acquisition value the value declared for ISD at death — which in practice often works similarly to a step-up because that ISD value becomes the new base. But the two mechanisms are not identical, they attach to different taxes, and mismatches arise. A Spanish-resident heir who inherits appreciated US stock enjoys the US step-up for US income tax, yet must still fit the asset into the Spanish ISD valuation and, on a later sale, into Spanish IRPF. Coordinating the death-date valuation across both systems is essential to avoid either an inflated Spanish gain or a US–Spain mismatch.
How are US citizens resident in Spain taxed at death?
This is the most exposed profile of all. A US citizen who lives in Spain is caught by both systems at once:
US estate tax: US citizens are subject to federal estate tax on their worldwide estate, wherever they live. Residency in Spain does not remove them from the US net; citizenship is the trigger.
Spanish ISD: because they are resident in Spain, their heirs (or, depending on the heirs' residence, the assets located in Spain) fall within Spanish ISD by personal obligation on the worldwide estate.
The saving grace is usually the size gap between the two thresholds. Below the US exemption, no US estate tax is due even though the worldwide estate is fully within scope; the real bill is Spanish ISD, softened or not by the applicable region's rebates. But for genuinely large estates that exceed the US exemption, both taxes can land, and the Article 23 / US foreign-tax-credit machinery becomes the only defence against paying twice.
How are Spanish-resident heirs of a US decedent taxed?
A very common situation: the parent lived and died in the United States, and the child lives in Spain. Here the child is a Spanish tax resident inheriting from a US decedent.
Because the heir is resident in Spain, they are liable to ISD by personal obligation on everything they inherit worldwide, including the US assets. The important — and often overlooked — point is that a non-resident or cross-border heir is entitled to apply the rules of the relevant autonomous community rather than being forced onto the harsher state default. Following EU case law and the Spanish reforms in the Second Additional Provision (Disposición Adicional 2ª) of the LISD, connections with non-EU countries such as the United States are now also brought within the regional-rules regime. In practice this means a Spanish-resident heir of a US parent can usually access the same generous regional reductions and rebates as a purely domestic heir — a point worth confirming for the specific community involved, because it can change the bill by tens of thousands of euros.
We cover this scenario end to end in our companion article on inheritance between the USA and Spain: applicable law, taxation and procedures.
How are inherited IRAs and 401(k)s taxed afterwards?
Retirement accounts are where cross-border estates most often go wrong. A traditional IRA or 401(k) is "pre-tax" money in the US: the original owner never paid income tax on it, so someone eventually has to. Inheriting one is not the end of the tax story — it is the beginning of it.
For US purposes, the account value at death counts for estate-tax scope, and separately every dollar the beneficiary later withdraws is ordinary income subject to US income tax (there is no step-up on this "income in respect of a decedent"). Under current rules, most non-spouse beneficiaries must empty the inherited account within about ten years, forcing large taxable distributions.
For a beneficiary resident in Spain, the same withdrawals must also be characterised for Spanish tax — genuinely complex, since it depends on whether the amounts are treated as employment/pension income or as returns on capital, with the income tax treaty's pension rules and saving clause in play. The headline risk is being taxed on the same distribution in both countries with imperfect credit relief. Model this before taking any distribution, not after.
What about US life insurance in a cross-border estate?
Life insurance is another classic trap because the two systems treat it in opposite ways. In the US, life insurance proceeds are generally free of income tax for the beneficiary and, if the policy is owned outside the insured's estate (for example through an irrevocable life insurance trust), can also be kept out of the taxable estate.
Spain is far less forgiving. Life insurance proceeds paid on death to a beneficiary are, as a rule, subject to Spanish ISD — they are pulled into the inheritance tax base (with a limited specific reduction for close relatives). So a US policy that the family assumes is "tax-free" can generate a Spanish ISD liability for a beneficiary resident in Spain. The characterisation of foreign policies, and of trust structures holding them, is delicate; we discuss it in our note on international inheritance taxation in Spain: foreign life insurance and trusts.
Which forms and deadlines apply on each side?
The compliance calendars are as different as the taxes themselves.
United States — Form 706: the federal estate tax return is filed by the estate, generally due nine months after death (with a six-month extension available). It is only required when the estate exceeds the filing threshold or when a surviving spouse elects to preserve the deceased spouse's unused exemption (portability). Even where no tax is due, filing may be advisable to fix values and preserve elections.
Spain — Modelo 650 (inheritance) or 651 (gifts): the heir files the ISD self-assessment. The deadline is six months from the date of death, and — this surprises US families every time — it is far shorter than the US window. A one-off extension of a further six months can be requested, but it must be applied for within the first five months. Missing the six-month deadline triggers surcharges and interest.
The mismatch between a nine-month US deadline and a six-month Spanish deadline is a practical headache: the Spanish return often falls due before the US probate has even produced final valuations. Managing that sequencing — sometimes filing a provisional Spanish return and adjusting later — is part of the job.
A worked example: the Miller family
Consider Robert Miller, a US citizen who retired to Marbella, and his daughter Sarah, who is a Spanish tax resident. Robert dies in 2026 with a worldwide estate of about 4 million dollars: a US brokerage account, a traditional IRA, a US life insurance policy, and an apartment on the Costa del Sol.
On the US side, Robert's 4-million-dollar estate is well below the federal exemption (around 13.6 million dollars as of 2026), so no federal estate tax is due — although a Form 706 may still be filed to establish values and portability. The brokerage assets receive a step-up in basis, wiping out decades of US capital gain.
On the Spanish side, Sarah is a Spanish resident inheriting worldwide, so she owes ISD on the whole 4 million, including the US assets. Because she can apply the rules of the autonomous community connected to the estate (Andalusia, where the apartment sits and where her father was resident), she benefits from the region's near-total rebate for children — dramatically reducing what would be a punishing bill on the state scale. The life insurance proceeds, tax-free in the US, are pulled into her Spanish ISD base. And when Sarah later draws down the inherited IRA, each distribution is ordinary income taxed in the US and must be run through the Spanish rules too. The lesson: no US estate tax, but a live and manageable Spanish exposure whose size turned entirely on getting the regional rules, valuations and withdrawals right.
What planning tools actually work?
Cross-border estate planning is not about a single clever trick; it is about aligning documents, law and timing across two systems. The tools that consistently earn their keep include:
Coordinated wills. Ideally a US will covering US assets and a Spanish will covering Spanish assets, drafted so they dovetail rather than accidentally revoke one another. A single all-in-one will drafted in one country routinely causes chaos in the other.
Professio iuris (choice of law). Under EU Regulation 650/2012, a national of a non-EU state such as the US can choose the law of their nationality (for example, the law of their US state of citizenship) to govern the succession. This governs who inherits and how the estate devolves — it does not change the tax — but it prevents Spanish forced-heirship rules from overriding US-style testamentary freedom.
Lifetime gifting. Because ISD taxes the recipient and the US taxes the transferor, well-timed lifetime gifts can shift value out of a future estate — but gifts have their own tax consequences on both sides (Spanish gift tax, US gift-tax rules and exemption use, and the loss of step-up), so they must be modelled, not assumed.
Valuation discipline. Fixing a consistent, defensible date-of-death value that works for Form 706, for ISD, and for the eventual step-up avoids both double taxation and later disputes.
Beneficiary and account structuring. Reviewing IRA beneficiary designations, life-insurance ownership, and any trusts before death, with an eye on how Spain will characterise them, is where the largest savings are usually found.
What are the most common mistakes?
Assuming the income tax treaty covers death taxes. It does not. There is no US–Spain estate or inheritance tax treaty.
Assuming a large American is safe because of the high US exemption. They may owe no US estate tax and still face a substantial Spanish ISD bill.
Missing the six-month Spanish deadline while waiting on US probate, and incurring surcharges.
Treating US life insurance as tax-free in Spain. It is generally caught by ISD.
Ignoring the deferred income tax on inherited IRAs and 401(k)s and the risk of double taxation on withdrawals.
Not claiming the Article 23 LISD deduction or the US foreign death-tax credit when both taxes genuinely apply.
Defaulting to the harsher state ISD rules when the more favourable autonomous-community rules were available.
Getting help with a US–Spain estate
Cross-border estates between the United States and Spain reward careful, early planning and punish improvisation. Because there is no death-tax treaty, the two systems will not coordinate themselves — someone has to do it, deliberately, on both sides. If you are a US citizen living in Spain, or a Spanish resident expecting to inherit from a US relative, a coordinated plan can be the difference between a manageable bill and paying twice.
If you would like to discuss your situation, you can reach me directly:
WhatsApp: https://wa.me/34644121802
Book a call: Schedule a consultation
Email: taxlegalspain@gmail.com
Disclaimer: This article is general information as of 2026 and is not legal or tax advice. Tax thresholds, exemptions and rules — including the US federal exemption and its possible reversion — change over time and depend on your specific circumstances and the law in force at the relevant date. Please seek tailored professional advice before acting.