The 31 December 2025 value, and why it usually helps you

The rule

Belgium's 10% capital gains tax applies to gains realized from 1 January 2026. Gains you accumulated before that date are not in scope.

The mechanism that delivers this is the step-up: for listed assets held before 2026, the acquisition value used to compute your gain is the last closing price of 2025, not the price you originally paid.

What that means in practice

Suppose you bought a world ETF at €52 in 2019. At the end of 2025 it closes at €118. You sell in 2026 at €112.60.

• Measured against what you paid, you made €60.60 per share.
• Measured against the step-up value, you made −€5.40 per share — a loss.

Only the second figure matters for this tax. Seven years of growth are simply outside the regime.

When the purchase price is used instead

If your evidenced historical cost is higher than the 31/12/2025 close, you may use it instead — an option available until 31 December 2030. This is the case for anything bought near a peak and still under water at the end of 2025.

"Evidenced" is doing real work in that sentence: keep the contract notes.

Why a missing 2025 price costs you money

If a tool cannot find the 31/12/2025 close for one of your holdings, it has to fall back to your purchase price. For a long-held position that price is usually much lower — so the computed gain, and the tax on it, come out too high.

Belfolio names every instrument it could not price rather than quietly showing you a larger number.

The ten-year rule

Separately, gains on assets held continuously for at least ten years are exempt under the general regime. That is measured per parcel, from the actual acquisition date — which is why per-lot records matter and a single average purchase price is not enough.

Always verify your figures

Belfolio computes and presents these amounts for information only. This is not tax advice. Verify them with the FPS Finance or your accountant before filing.