FIFO Cost Basis Crypto Belgium: How Cryptotax Calculates Your Capital Gains

FIFO determines how much tax you pay on your crypto gains. In this guide we explain how lot matching works, how your cost basis stays intact across bridges, and what you export for your accountant.

🔍 What is FIFO and why does Belgium require it?

FIFO stands for First In, First Out: the first crypto you bought is deemed to be the first sold. Belgium accepts this method as the standard for calculating capital gains on crypto assets. Consistency is essential - the tax authority expects you not to switch methods every year.

Since 1 January 2026 a capital gains tax of 10% applies to crypto gains above the annual exemption of €10.000. That calculation starts from the cost basis of each lot, and FIFO determines which lot is used first.

⚙️ How lot matching works in Cryptotax

Cryptotax processes your taxable events per asset in chronological order. At every disposal, the engine assigns the volume to the oldest open acquisition lot - the FIFO principle. If one lot is not sufficient, the assignment continues to the next oldest lot, until the full disposal amount is covered.

• Wallets and exchanges together - Lots from all your connected sources are evaluated in the same FIFO order.
• Lot-level links - Each assignment creates a link between the disposal and the source acquisition, with timestamp, account, quantity, and cost basis.
• Partial lots - If you sell only part of a lot, only that part is assigned. The remainder stays open for future disposals.

🌐 Cross-chain cost basis: bridges without a broken history

When you bridge ETH from Ethereum to Base, your cost basis must not be lost. Cryptotax links the deposit and withdrawal legs of a bridge into a single continuity flow. This keeps the original acquisition price intact, regardless of which chain the asset is on.

• Bridge deposit and withdrawal are matched on timing and value.
• Matched events share continuity context, so the lot basis flows through correctly.
• Bridge fees are linked to the same flow for auditability.

Read more about how bridging affects your cost basis in our article Bridging and cross-chain fees, or discover how we recognise transfers between your own accounts via transfer matching.

💡 Worked example: the step-up rule and FIFO in action

Suppose you made three purchases:

On 31 December 2025 the ETH price was €3.400. Under the step-up rule, the tax cost basis of the pre-2026 lots is stepped up to that reference date:

You now sell 2,5 ETH in April 2026 at €4.000 per ETH (proceeds: €10.000). FIFO assigns as follows:

Total capital gain: €1.500. This falls within the annual exemption of €10.000, so no tax is owed in this example. Without the step-up, the basis would have been lower and the capital gain higher - the step-up protects your historical gains.

📊 What you export for your accountant

The disposals CSV from Cryptotax is lot-level. Each row represents one FIFO assignment and contains:

• Disposal and acquisition timestamps
• Holding period
• Assigned cost basis and proceeds
• Resulting gain or loss per lot-link
• Year totals in the summary row

This is useful for accountant review, reconciliation, and as evidence of the build-up of each disposal. Read more about our export options.

🧾 Summary

✅ Try it today

Want to see how FIFO is applied to your transactions? Connect your wallets for free and view your lot-level report in the dashboard. Accountants can share audit-ready exports with their clients via the partner programme.

⚠️ Disclaimer: This article is informational only and does not constitute individual tax advice. For specific cases, consult a certified Belgian tax adviser or request a ruling from the Dienst Voorafgaande Beslissingen.