The question, and why it matters
Since 2026, Belgium taxes realised gains on crypto at 10% — the full framework is in the article on crypto tax in Belgium in 2026. On a sale for euros, the realisation is obvious. But most crypto transactions are not sales for euros: they are swaps — ETH to BTC, an altcoin to a stablecoin, and back. Whether each of those swaps is a taxable event determines, for an active portfolio, almost the entire size of the return.
What most sources say
The prevailing reading is that every realisation is a taxable event, and that a swap realises the gain on the coin you give up — even without any stop in euros. The same holds when you pay for something directly in crypto.
An example. You swap an ETH position into BTC at a moment when it is worth €5,000. Your starting value for that ETH — purchase price, or the 31 December 2025 step-up value for what was bought before 2026 — is €4,200. On that reading you realise €800 of gain at that moment, and the BTC you receive starts with €5,000 as its new starting value.
How that starting value and the annual exemption fit into the full sum is covered in the step-by-step guide to calculating crypto capital gains tax.
What is not confirmed
At the time of writing, the FPS Finance has not confirmed in detail how coin-to-coin swaps are treated. No circular says every swap is a realisation, and none says otherwise. Nor is it confirmed that crypto falls entirely under the same regime as shares and ETFs; someone who trades fast and systematically — and frequent swapping can point that way — may fall under the speculator or professional regime, with different rates.
So you will read no certainty here, because there is none. Sites that present a single reading as settled, without reservation, are running ahead of the administration.
What to do today
The practical conclusion does not depend on how the question lands: record the euro value of every swap at the moment of the swap. If the strict reading prevails, your calculation is ready; if the lenient one prevails, you have at worst over-documented. The reverse does not work — a euro price from months ago is hard to substantiate after the fact.
Your exchange's export is the source for this; the per-exchange export guide says, platform by platform, what the file does and does not contain. The calculator reads that history and sets each swap apart — named as a swap, without sticking an invented euro value on it when the file contains none.
To be confirmed. The treatment of coin-to-coin swaps, of swaps into stablecoins, and of staking, mining and airdrops has not been confirmed in detail by the FPS Finance at the time of writing. Treat any figure that rests on it as uncertain.
Verify your figures
Belfolio describes the state of the discussion here, not settled law. This is not tax advice. Check your situation with the FPS Finance or your accountant before filing.
Published 29 Aug 2026
Frequently asked questions
- I swapped ETH for BTC without ever seeing euros. Is that taxable?
- According to most sources, yes: every realisation is a taxable event, and a swap realises the gain on the coin you give up. You need the euro value at the moment of the swap. The FPS Finance has not confirmed this in detail — treat it as uncertain, but record it.
- What about a swap into a stablecoin?
- A stablecoin is legally not euros, so on the reading where every swap is a realisation, that also holds for a swap into USDC or USDT. Here too there is no explicit confirmation from the administration.
- What if the rules end up landing differently?
- Whoever recorded the euro value of every swap can handle any reading. Whoever recorded nothing cannot reconstruct afterwards what a swap was worth at that moment. Recording is the only choice that wins in both scenarios.