If you sold US stocks or ETFs at a gain in Belgium between June 1 and August 31, 2026, a decision attached to that sale has a deadline of August 31, 2026 - a few weeks from when this update was written. Belgium’s new 10% capital gains tax, in force since January 1, 2026, is by default withheld automatically by the broker. You can instead opt to settle it yourself through your annual tax return - but you have to tell your financial institution that in writing, unambiguously, by that date, and the choice is binding for the rest of the year on that account. Miss it and the broker’s default withholding stands for the remainder of 2026.
That deadline is the most time-sensitive item in this guide, so it comes first. Everything else - the 15% treaty rate on dividends, the précompte mobilier, a newly relevant €833 annual dividend exemption, and the mechanics of the capital gains tax itself - follows below.
The New Capital Gains Tax: What’s Actually Due, and When
Belgium introduced a 10% tax on realized capital gains from financial assets, effective January 1, 2026. The law was adopted by the Belgian Parliament on April 3, 2026 and published in the Belgian Official Gazette on April 21, 2026 - both dates later than the tax’s own effective date, which is why the rollout has a staggered withholding mechanism rather than a clean start.
The three periods that matter for 2026:
- January 1 - May 31, 2026: no withholding tax obligation applied, because the legislation hadn’t been formally approved yet. Any gains realized in this window are settled entirely through the annual personal income tax (PIT) return - there was nothing for a broker to withhold at the time.
- June 1 - August 31, 2026: brokers can apply automatic withholding on realized gains, but an individual investor can opt out in writing, by a deadline the broker sets no later than August 31, 2026, and instead settle the tax via the annual return. Opting out for a given account or product is binding for the rest of 2026 - it cannot be switched back mid-year.
- From September 1, 2026 onward: the standard mechanism applies - brokers withhold 10% at source by default unless a valid opt-out is on file for that account.
The rate and exemption: capital gains on financial assets - shares, ETFs, and similar instruments held as part of normal private wealth management - are taxed at 10%. The first €10,000 of gains per taxpayer per year is exempt (€20,000 for a married couple or legal cohabitants filing together).
The exemption isn’t just €10,000 - it can grow to €15,000 with no action beyond simply not using it. Up to €1,000 of an unused annual exemption carries forward, on a five-year, first-in-first-out basis. An investor who realizes, say, €900 in gains in one year uses only part of that year’s exemption - the unused €100 (capped at €1,000 regardless of how much of the exemption actually went unused) rolls into next year’s allowance. Carried forward consistently over five years, this can lift an individual’s effective exemption to €15,000 (€30,000 for a couple) without requiring any gains to be realized at all in the interim - it accrues from simply not selling.
Historical gains are protected. Only appreciation from January 1, 2026 onward is taxable. For any position held before that date, the acquisition cost for calculating the taxable gain is reset to the position’s market value on December 31, 2025 - meaning years of pre-2026 appreciation are simply never taxed under this regime.
Losses can only offset gains realized in the same year and the same category; they cannot be carried forward.
Who this doesn’t reach: the tax applies to Belgian resident individuals conducting normal private wealth management. It does not apply to gains connected to a professional activity, which follow separate, pre-existing rules.
Sequencing Gains Around the Exemption - Including the Carry-Forward
Because the exemption is annual rather than lifetime, and because the December 31, 2025 step-up in cost basis wipes out years of pre-2026 gains, the practical planning question for 2026 and beyond is less “should I sell” and more “how much should I realize in a given year - and does leaving room this year buy a larger exemption later.”
Illustration: a position bought in 2022 for €15,000, worth €26,000 on December 31, 2025, and sold in 2026 for €29,000. The taxable gain under the new regime is €29,000 - €26,000 = €3,000 - the €11,000 of appreciation that happened before 2026 is excluded entirely by the step-up. If this is the only capital gain realized that year, it falls well within the €10,000 exemption and no tax is owed regardless of which withholding period the sale falls into.
An investor holding a large position with substantial 2026-and-later appreciation is better served selling in tranches across multiple years - realizing close to but under €10,000 in net gains annually - than triggering one large disposal that pushes well past the exemption in a single year. And for an investor who realizes little or nothing in a given year, the carry-forward means that inaction isn’t wasted: up to €1,000 of that year’s unused exemption banks toward a future year, so someone who holds off selling for several years in a row can arrive at a later disposal with an exemption meaningfully above €10,000 - up to the €15,000 individual ceiling (€30,000 per couple) after five years of consistent carry-forward.
The €833 Dividend Exemption Most Guides Miss
Separately from the capital gains changes, Belgium provides an annual €833 exemption (2026, income year 2026 / tax year 2027) on dividend income for individuals - and it applies to both Belgian and foreign dividends, including US dividends, per the Belgian finance ministry’s own guidance.
This exemption is not automatic. For dividends where Belgian précompte mobilier was withheld, it’s claimed via specific codes on the tax return. For foreign dividends - the typical case for US stocks held directly - there’s no Belgian withholding to reconcile against, so the mechanism is simpler in practice: the first €833 of the gross foreign dividend amount is simply left off the declared total. Belgium’s tax administration cannot pre-fill this for you on a simplified return; it requires a manual correction via MyMinFin or the paper return.
For an investor receiving, say, €1,200 in US dividends over the year, only €367 needs to be declared as taxable dividend income after applying the exemption - a detail that’s easy to miss because nothing about the broker’s withholding or the pre-filled return surfaces it automatically.
The Treaty: Dividend, Interest, and Capital Gains Rates
The current US-Belgium treaty is the Convention Between the Government of the United States of America and the Government of the Kingdom of Belgium for the Avoidance of Double Taxation and the Prevention of Fiscal Evasion with Respect to Taxes on Income, signed November 27, 2006, in force from December 28, 2007.
| Income Type | Without Treaty | Portfolio Rate | Pension Fund | Direct Corporate (80%+) |
|---|---|---|---|---|
| US dividends to Belgian resident | 30% | 15% | 0% | 0% |
| Belgian dividends to US resident | 30% | 15% | 0% | 0% |
| Interest (either direction) | 30% | 0% | 0% | 0% |
| Royalties (either direction) | 30% | 0% | 0% | 0% |
| Capital gains - securities | Varies | Residence country only | Residence country only | Residence country only |
Source: US-Belgium Income Tax Convention (November 27, 2006); US Senate Executive Report 110-2; IRS Publication 515 (2026).
Interest at 0% and pension fund dividends at 0% are the treaty’s most favorable features - matching the US-UK and US-Germany treaties and better than the US-Canada treaty’s RRSP mechanism, which caps rather than eliminates withholding. The 0% pension rate applies to qualifying Belgian pension entities (OFPs, IBPs, and similar regulated vehicles) as beneficial owners - not to an individual’s personal brokerage account, which gets the standard 15% portfolio rate.
Article 13 gives Belgium exclusive taxing rights over capital gains from selling US securities - no US withholding applies at the point of sale, which is exactly why the new domestic 10% CGT described above, not the treaty, is what actually determines the tax on those gains.
Dividends: The 15% Rate and Précompte Mobilier
US side: without a W-8BEN on file, the default 30% withholding applies. With the form filed and the treaty claimed under Article 10, withholding drops to 15%.
Belgian side: US dividends received in a Belgian brokerage account are also subject to Belgium’s own withholding tax - the précompte mobilier (or roerende voorheffing) - at 30% of the gross amount, with the US withholding creditable against it.
Worked example:
| Amount | |
|---|---|
| Gross US dividend | $2,400 |
| US withholding at 15% | -$360 |
| Net received from broker | $2,040 |
| Belgian précompte mobilier at 30% on gross | $720 |
| Credit for US withholding already paid | -$360 |
| Net Belgian withholding due | $360 |
| Total tax (US + Belgium) | $720 (effective 30% on the gross) |
For most Belgian individual investors, the précompte mobilier is a final tax - no further reporting is required once it’s correctly applied, aside from claiming the €833 exemption described above where applicable. One exception: if total taxable income is modest enough that the marginal federal rate falls below 30% (the lowest federal bracket starts at 25%, on income up to €16,320), declaring dividend income voluntarily and claiming credit for the précompte mobilier withheld can reduce the effective rate from 30% to the lower marginal rate - an option worth checking for lower-income investors specifically, though for most investors at higher brackets the flat 30% final tax is simpler and no worse.
Because dividends face this 30% combined rate while accumulating ETFs defer that tax entirely until a taxable event, many Belgian investors favor accumulating over distributing structures for US equity exposure - though from 2026, deferred gains eventually meet the new 10% CGT rather than escaping tax altogether the way they did before this year.
Filing Your W-8BEN from Belgium
Belgian brokers vary in how they handle Form W-8BEN:
- Interactive Brokers: collected at account opening; reliable at applying the reduced rate.
- Bolero (KBC): required for US equity trading, submitted during account registration.
- Saxo Bank Belgium: completed at onboarding for US market access.
- Keytrade Bank: required for US stocks, submitted at account setup.
- Degiro: process varies - verify directly that the form is on file by checking dividend statements.
Verification: 15% on a dividend statement confirms the treaty rate is active; 30% means the form is missing or has lapsed. The form is valid for three calendar years from signing and brokers do not always send renewal reminders, so set your own.
The Reynders Tax: A Separate Layer for Mixed Funds
Belgian investors in funds that hold a meaningful bond component face a third tax layer alongside précompte mobilier and the new CGT: the Reynders Tax (taks op de meerwaarden van fondsen / taxe sur les plus-values des fonds).
This applies specifically to the fixed-income portion of gains realized on selling or redeeming units in mixed or bond funds - both accumulating and distributing - at a 30% rate. Pure equity funds, where the fixed-income component stays below 10% of assets, generally fall outside its scope. A global equity ETF with negligible bond exposure is not affected; a balanced fund holding both stocks and bonds faces the Reynders Tax on the bond-attributable gain and the new 10% CGT on the equity-attributable gain, as two separate calculations on different portions of the same disposal. Belgian brokers are generally responsible for calculating and applying both at the point of sale - checking the transaction confirmation for how each component was taxed is worth doing rather than assuming.
How the US-Belgium Treaty Compares
| Country | US Dividends (Portfolio) | Interest | Capital Gains | Pension Exemption |
|---|---|---|---|---|
| Belgium | 15% | 0% | Residence only | 0% |
| United Kingdom | 15% | 0% | Residence only | 0% in qualifying SIPP |
| Germany | 15% | 0% | Residence only | Pension exemption exists |
| Austria | 15% | 0% | Residence only | 0% (Pensionskassen) |
| Denmark | 15% | 0% | Residence only | 0% |
| Japan | 10% | 0% | Residence only | Yes |
The treaty rates put Belgium squarely alongside the UK, Germany, Austria, and Denmark - none of them stand out from each other at the treaty level. What actually separates a Belgian investor’s outcome from an investor in most of these other countries is domestic law layered on top: the 30% précompte mobilier makes Belgium’s effective dividend tax noticeably higher than a UK investor’s ISA-sheltered dividends or a German investor’s 25% flat Abgeltungsteuer, while the new 10% CGT (with its €10,000 exemption and 2025 valuation step-up) is a genuinely new variable none of these comparison countries share in the same form.
The Belgium Investor’s Running List
The Belgian investor’s short list:
- Confirm W-8BEN is on file - check for 15%, not 30%, US withholding on dividend statements, and renew before the three-year expiry
- Verify the broker is crediting US withholding against the Belgian précompte mobilier rather than deducting both in full (effective total should be 30% on the gross, not 45%)
- Claim the €833 annual dividend exemption on foreign (US) dividends - not automatic, and not pre-filled by the tax administration for foreign-source income
- Document December 31, 2025 values for every US stock or ETF position held before that date - this is the cost basis for the new CGT
- For gains realized June 1 - August 31, 2026: decide by August 31, 2026 whether to opt out of automatic broker withholding in favor of settling the 10% CGT via your annual return - the choice is binding for the rest of the year on that account
- Plan gain realizations across the €10,000 annual CGT exemption rather than triggering one large disposal in a single year, and track unused carry-forward (up to €1,000/year, five-year FIFO, €15,000 individual ceiling) if realizing little or nothing in a given year
- If holding a mixed or bond fund: check transaction confirmations for whether the Reynders Tax (bond component) and the new CGT (equity component) were both applied correctly
US citizen living in Belgium:
- File Form 1040 annually, including Belgian income, dividends, and capital gains
- Claim Foreign Tax Credit (Form 1116) - Belgian rates are generally high enough that the FTC eliminates most additional US federal tax
- File FBAR (FinCEN 114) if aggregate Belgian account balances exceed $10,000 at any point
- File Form 8938 above the applicable FATCA threshold for residents abroad
- Avoid Belgian-domiciled funds (SICAVs, Belgian ETFs) where PFIC rules would apply; prefer US-domiciled ETFs or direct stocks
- Track Belgian CGT paid separately from précompte mobilier - it may generate its own Form 1116 credit
What Changed, and What Didn’t
The treaty side of this hasn’t moved: 15% on dividends with a W-8BEN filed, 0% on interest, capital gains reserved to Belgium under Article 13. That part has been stable since 2007 and needs no active decisions beyond keeping the form current.
2026 changed the Belgian domestic side substantially. The 10% capital gains tax is real, retroactive to January 1, and - for anyone who sold between June and August - attached to a decision with an August 31, 2026 deadline that has nothing to do with the treaty and everything to do with how the new law was rolled out mid-year. The €833 dividend exemption has quietly applied to US dividends the whole time and is worth claiming on every return going forward. Between the précompte mobilier, the new CGT, and the Reynders Tax on mixed funds, Belgium now has more moving domestic parts than most countries in this series - which makes getting the account and filing mechanics right worth more than usual.
An overview of investing from Belgium, not a recommendation for your circumstances. Rates are based on the US-Belgium Income Tax Convention (November 27, 2006). The Belgian capital gains tax was adopted by parliament on April 3, 2026, published in the Belgian Official Gazette on April 21, 2026, and applies retroactively from January 1, 2026. Belgian and US tax rules change, and the CGT withholding mechanics in particular remain new enough that broker implementation may vary. Always consult a qualified cross-border tax professional on the specifics of your own holdings.
Sources: US-Belgium Income Tax Convention (November 27, 2006); US Senate Executive Report 110-2; IRS Publication 515 (2026); SPF Finances (Belgian Federal Public Service Finance) - dividend exemption guidance (2026); KPMG Belgium - Belgian Capital Gains Tax Approved by Parliament, Royal Decrees on Belgian Capital Gains Tax Published, and GMS Flash Alert 2026-160 (2026); PwC Belgium - Belgium’s Comprehensive Capital Gains Tax Changes (2026); EY Belgium - The New Belgian Capital Gains Tax: What Changes in 2026; RSM Belgium - Law Introducing a Capital Gains Tax on Financial Assets (2026); Grant Thornton Belgium - Belgium’s New Capital Gains Tax: What You Need to Know (2026); Fieldfisher - Belgium Introduces Capital Gains Tax on Financial Assets as from 1 January 2026; Loyens & Loeff - Capital Gains Tax in Belgium Becomes Reality as of 1 January 2026; Taxpatria - Opt-in or Opt-out, That’s the Question (2026); FinCEN FBAR guidance (2025); IRS Form 8938 FATCA thresholds (2025 tax year).
