Capital gains tax across the Netherlands and Belgium: why predictable execution matters more than the rate

By Frank Schooneveldt, Managing Director Akkuro Savings & Investments

The introduction of a Belgian capital gains tax is part of a broader European shift: more targeted taxation of realized gains, combined with maintaining or recalibrating existing regimes in countries such as France, Italy, Spain and the United Kingdom. It is tempting to narrow the debate to rates and effective dates, yet the real questions are neutrality, execution simplicity and transparency for long‑term investors. The European perspective is essential because it shows how different systems are moving toward the same goal: predictable, workable rules that inform investors rather than surprise them. 

Netherlands: no general tax on realized gains, but box 2 for substantial shareholdings

In the Netherlands, most retail investors do not pay tax on realized gains. Their portfolios fall under box 3, which uses a deemed‑return approach. Investors with a substantial interest of at least 5 percent are treated differently. They fall under box 2, where dividends and disposal gains are taxed. From 2026, the rate is 24.5 percent up to 68,843 euros and 31 percent above that amount. This split matters because it shapes how different investment structures are taxed in practice. 

Netherlands box 3: toward actual‑return taxation (from 2028)

Beyond Belgium’s reform, the Netherlands is preparing a structural shift in box 3 from a deemed‑return model to taxation of actual returns. The government’s Wet werkelijk rendement box 3 proposes a hybrid system: in principle an accretion‑based tax on actual returns (income plus unrealized gains/losses), with realization‑based taxation for specific assets such as real estate and shares in start‑ups. The bill provides for a tax‑free results threshold and loss carryforwards above a small annual floor. It was submitted to Parliament on May 19, 2025; following the 2024 delay, the target start date is January 1, 2028, with transitional years continuing the current deemed‑return regime (including the “actual return” rebuttal option). Operationally, this shift is material for data quality, year‑end valuations and loss tracking, and it will require clean interfaces between banks/brokers and the tax administration.

Belgium: from exemption to a 10% tax on realized gains, with layered complexity due to Reynders

Through 2025, gains under normal private portfolio management were generally exempt. From January 1, 2026, Belgium plans a 10% tax on realized gains on financial assets (including crypto), alongside the continuing Reynders tax. This dual structure introduces operational complexity: Reynders takes priority and its base is deducted from the new capital‑gains base to prevent double taxation, while funds invested 100% in bonds and already in scope of Reynders are exempt from the new capital gains tax. The regime also introduces a step‑up at the December 31 2025 close an opt‑out for self‑filing, and six additional months for banks to implement automated withholding, with potential retroactive collection from January 1, 2026. 

The core principles: neutrality, operational simplicity and transparency

Neutrality requires equal treatment of equal outcomes. The Dutch split between box 3 (deemed return) and box 2 (substantial shareholdings) is internally consistent. In Belgium, Reynders‑priority reduces double taxation risk, but running two regimes side by side challenges neutrality and increases administrative complexity. Simplicity argues for a single, clearly defined base and sequence of rules. Transparency requires continuous, auditable views of bases, allowances and interactions, especially when retroactive collection applies. 

European context and implications

France is reconsidering exemptions on primary residences and tightening rules for non‑residents; Italy’s Budget Law 2026 resets thresholds for dividend relief and the participation exemption (PEX) on capital gains; Spain is removing inflation/indexation adjustments, which increases the nominal base; and the UK is raising CGT rates and lowering the annual exemption. Across these changes, the emphasis is on transparency, loss offsetting and operational feasibility. For cross‑border investors, fiscal stability is less of a given, which makes documentation, data quality and timing more important. 

Europe’s FTT debate: a long‑running effort, with national workarounds

The Financial Transaction Tax (FTT) has been debated at the EU level for more than a decade. The European Commission’s 2026 Work Programme confirms that the proposal to pursue the FTT under enhanced cooperation has been withdrawn, which explains why Member States continue to act nationally. In practice, several countries already levy their own transaction taxes: France raised its FTT rate to 0.4% in 2025, Italy’s 2026 Budget Law adjusts the Italian FTT alongside broader capital‑market measures, and Spain continues to operate its national FTT with updated procedures and in‑scope listings published by the tax agency. For Dutch stakeholders, this matters because any renewed domestic FTT discussion sits within a fragmented European landscape; broker guidance reflects this mosaic and the operational burden that comes with divergent scopes and rates. A coordinated EU solution would reduce frictions and improve comparability across markets until then, firms need clear, consistent rules per jurisdiction and transparent reporting across regimes. 

From policy to practice: capital gains tax without friction

Planning ahead requires reliable data, clear tax bases and proven calculation logic. In Belgium, the Akkuro platform withholds from the first euro under the new capital gains tax. We do not apply the €10,000 annual allowance (with a step‑up to €15,000 if unused) at source. Any relief or refund related to that allowance must be claimed via the Belgian tax return by the client. In our calculation engine for SemmieWealth and ING, we:

• Use the December 31, 2025 close as the reference for pre‑2026 positions (step‑up),

• Apply Reynders priority first and deduct the Reynders base from the capital‑gains base to avoid double taxation,

• Support opt‑out choices that shift withholding to self‑reporting for the remainder of the year,

• And keep full audit trails for retroactive settlement once legislation is finalized (effective January 1, 2026).

If the Dutch box 3 bill is enacted for 2028, we will align data capture and reporting for actual‑return components (income, year‑end valuations, realized/unrealized changes, and loss tracking) to support client reporting and tax files, while keeping the current deemed‑return years (including the “actual return” rebuttal) consistent through 2027. 

Our position on design

Operating two regimes in parallel, as in Belgium, may serve policy aims but adds layers for investors and intermediaries. Our preference is uniform, single‑layer taxation with limited exceptions and where possible, cross‑country alignment on how bases, priorities and allowances are computed and settled. That design reduces operational risk, enhances transparency and helps investors understand their net outcomes across markets.