Opt-in or opt-out for the capital gains tax: do you need to choose for your crypto?

Last updated: 25 May 2026 · Reading time: 8 minutes

In late May 2026, many investors receive a message from their bank: choose opt-in or opt-out for the new capital gains tax, and do it quickly. KBC asks for a decision by 28 May, Bolero by 29 May, BNP Paribas Fortis by 31 May. It is only natural that crypto investors wonder: do I need to make a choice for my crypto? The short answer is reassuring and surprising at the same time: for your crypto, that choice does not exist. You always declare your crypto capital gains yourself. This guide explains what opt-in and opt-out are, why they do not apply to crypto, and why that can work in your favour.

The capital gains tax law was approved by Parliament on 3 April 2026 and published in the Belgian Official Gazette on 21 April 2026 (Act of 6 April 2026). The rate is 10% on realised capital gains above an exemption of EUR 10.000 per person per year.

📌 What exactly is opt-in and opt-out?

Opt-in and opt-out are about who collects the tax, not about whether you owe it. The tax is 10% in both cases. The difference lies in the collection.

Opt-in (withholding at source). Your bank or investment platform automatically withholds 10% on every profitable sale and remits it to the tax authority. This is similar to the withholding tax on dividends and interest you already know today. Advantage: no administration, no surprise at tax return time. Disadvantage: the bank does not automatically apply your EUR 10.000 exemption or any losses you have, so you often pay too much and must reclaim the difference later via your tax return.

Opt-out (self-declaration). The bank withholds nothing. You declare your capital gains yourself in your tax return and immediately apply your exemption, your loss offset, and your historical cost basis. Advantage: full control and no unnecessary advance payment. Disadvantage: you must keep your own records and ensure you can pay the amount.

A few rules for the bank choice: it applies per securities account and is fixed for a full calendar year (changes are only possible from 2027). For joint accounts, all account holders must agree. And importantly: the automatic withholding at source only starts on 1 June 2026. Capital gains you realised between 1 January and 31 May 2026 must in any case be declared yourself.

🪙 The key point: for crypto the choice does not exist

Withholding at source requires a withholding agent: a Belgian bank or investment firm that can deduct the 10% before the money reaches your account. For crypto, no such intermediary exists. Crypto exchanges, whether Belgian or foreign, do not withhold Belgian capital gains tax. There is therefore nobody who can withhold on your behalf, and consequently nothing to choose.

The law confirms this explicitly. Regardless of whether you choose opt-in or opt-out on your securities account, you must always declare yourself for:

In other words: for your crypto you are by definition opt-out. You do not need to notify any bank, and no bank deadline at the end of May applies to your crypto. The choice your bank presents to you relates only to the shares, funds, and ETFs you hold at that bank.

✅ Why "always opt-out" actually works in your favour

Having no choice sounds like a restriction, but for anyone whose records are in order, opt-out is generally the most favourable system. That is precisely why many active investors choose it deliberately, even for their shares. When you self-declare, you immediately apply three things that withholding at source ignores:

• Your exemption of EUR 10.000 per person per year. This is indexed annually. The unused portion can be carried forward to a limited extent: up to EUR 1.000 per year in which you do not use the exemption, for a maximum of five years, up to a ceiling of EUR 15.000. The condition is that you do not touch the first EUR 1.000 of your basic exemption in that year. Read the details in our guide on the EUR 10.000 exemption.
• Your loss offset. Losses within the same category and the same year may be offset against your gains. With withholding at source, you would pay 10% on every profitable sale without your losses being taken into account.
• Your correct cost basis. For crypto you held before 2026, you use the step-up value (market value on 31/12/2025) or, if higher and provable, your actual purchase price. Withholding at source would not take this into account. Read how that works in our guide on the step-up rule.

With opt-in you would have to correct all of this afterwards via your tax return, with an excessive advance payment and a refund that can take months. With crypto you skip that detour: you settle correctly straight away.

⚠️ Important if you also hold a Belgian securities account

Do you hold shares, funds, or ETFs on a securities account at a Belgian bank in addition to your crypto? Then the opt-in/opt-out choice does apply there, and the end-of-May deadlines are relevant for that part of your portfolio. The law sets a general deadline of 31 August 2026, but banks ask for your decision much earlier so their systems are ready for the withholding from 1 June.

If you miss your bank's deadline, opt-in automatically applies for the full calendar year. Always verify the exact date with your own bank, as it can differ by one day per institution. For your crypto nothing changes: that remains self-declaration.

🛠️ What you concretely do need to do for your crypto

No bank choice does not mean "do nothing". Because you always declare your crypto yourself, the full burden of proof and calculation rests with you. This is the practical checklist:

• Record your snapshot. Document the market value of each crypto asset on 31 December 2025. That is your new fiscal cost basis (the step-up). Without evidence you risk the tax authority falling back on your original purchase price or even EUR 0.
• Keep track of your transactions. For crypto purchased after 2025, your actual purchase price (including fees) applies, and FIFO is mandatory for matching sales to purchases. For pre-2026 positions, the weighted average acquisition value per asset applies.
• Calculate your capital gain per year. Only the net amount above your exemption of EUR 10.000 is taxable at 10%.
• Declare via Tax-on-Web. You enter crypto capital gains yourself in your tax return. Read our guide on how to declare crypto in Belgium via Tax-on-Web.

Cryptotax automates exactly that self-declaration that crypto requires of you: it connects your exchanges and wallets read-only, freezes your 31/12/2025 snapshot, calculates your capital gain with the correct cost basis and loss offset, and delivers a substantiated report for your tax return. Start a free scan to see where you stand.

❓ Frequently asked questions

Do I need to do anything for my crypto before the bank deadline at the end of May?
No. The opt-in/opt-out deadlines of KBC, Bolero, BNP, and other banks apply only to securities accounts at those banks. Nothing changes for your crypto: you declare yourself regardless.

Will there ever be withholding at source on crypto?
Not under the current law. Withholding at source requires a Belgian withholding agent, and that does not exist for crypto. Crypto exchanges do not withhold Belgian capital gains tax.

What if I trade via a foreign broker (for example a crypto platform abroad)?
Foreign brokers do not withhold anything in any case. There too you have no opt-in/opt-out choice and you declare yourself in your Belgian tax return.

Does my crypto count towards the EUR 10.000 exemption?
Yes. The exemption of EUR 10.000 per person per year applies to your realised capital gains on financial assets, crypto included. You must claim the exemption yourself via your tax return; it is never applied automatically.

What about a joint situation, such as crypto I hold together with my partner?
Each taxpayer has their own exemption of EUR 10.000. For the bank choice on securities accounts, joint account holders must choose the same option, but for crypto there is no bank choice, so each of you declares your share of the capital gain.

I already realised a crypto gain in January 2026, before 1 June. Do I need to declare it?
Yes. Crypto capital gains are always declared by yourself, regardless of the date. The start date of withholding at source on 1 June 2026 only concerns withholding by banks on securities accounts.

📋 Summary

• Opt-in means your bank withholds 10% at the source, opt-out means you declare yourself. The choice applies per securities account and is fixed for a calendar year.
• For crypto that choice does not exist: there is no withholding agent, so you always declare your crypto capital gains yourself. The same applies to foreign securities accounts, foreign currency, and physical gold.
• That "always opt-out" works in your favour: you immediately apply your EUR 10.000 exemption, your loss offset, and your step-up cost basis.
• If you also hold shares or ETFs at a Belgian bank, the choice does apply there, with end-of-May deadlines (KBC 28 May, Bolero 29 May, BNP 31 May). Miss those and opt-in applies automatically.
• For your crypto the message remains: document your 31/12/2025 snapshot, keep track of your transactions, and declare correctly. Cryptotax automates that completely.

Further reading on the capital gains tax on crypto, the step-up rule, and the complete 2026 overview.

Sources:

• Bill DOC 56 1244/001: Act on the capital gains tax on financial assets
• d&p: Capital gains tax, opt-in or opt-out before 1 June
• Bolero: withholding at source ("opt-in") and opt-out
• BNP Paribas Fortis: ten questions about the capital gains tax
• Test-Aankoop: withholding at source or opt-out, you must make a choice

Disclaimer: This article is informational only and does not constitute individual tax advice. The capital gains tax law was approved on 3 April 2026 and published in the Belgian Official Gazette on 21 April 2026 (Act of 6 April 2026). Bank deadlines may change; verify them with your own institution. Consult a recognised Belgian tax adviser for specific cases.