It is one of the questions clients ask us most: “If Bitcoin was created to be anonymous and decentralised, how can the Spanish tax agency force me to report it? And worse still, why are you asking me for the full history since I started trading five years ago?”
The short answer: the tax agency wants to put an end to crypto anonymity. And to calculate your tax properly, past years weigh just as much as the current one.
This article explains the three mechanisms that have dismantled anonymity (Modelo 172, Modelo 173 and the DAC8 directive) and why the FIFO method obliges you to hand over your full traceability for the report to be correct.
The myth of crypto anonymity
When Bitcoin took off, investors settled on an idea that has stuck ever since: “if it is on a blockchain, nobody can know who I am”. In a way that was true: a wallet address is just a string of characters, with no name attached.
But that is not where the problem lies. Except for the very small minority who trade purely peer-to-peer and in a decentralised way, every other investor leaves a perfectly identifiable trail. And the tax agency does not need to break the blockchain to find you: it is enough to know:
- which exchange you used (Binance, Coinbase, Bit2Me, Kraken…)
- which bank transfers you made to those exchanges
- which wallet received funds from your verified (KYC) account
And that is where Modelo 172, Modelo 173 and DAC8 come in.
The three mechanisms that ended anonymity
1. Modelo 172: balances on Spanish exchanges
Exchanges based in Spain (such as Bit2Me) are required to file Modelo 172 with the tax agency. Once a year, that form reports:
- The full identity of every Spanish client (name, tax number, address)
- The balance of each coin as at 31 December, valued in euros
In other words: if you hold 0.5 BTC on Bit2Me at year end, the tax agency knows it without you saying a word. This is not information that “can” be requested, it is information the exchange must hand over as a matter of course.
2. Modelo 173: transactions carried out during the year
Modelo 173 complements the 172 with the full transaction detail:
- Purchases and sales of crypto
- Swaps (exchanging one coin for another)
- Payments received and made in crypto
For each transaction, exchanges have to report the date, the counterparty and the value in euros. The AEAT ends up with a complete X-ray of your activity on Spanish exchanges, with or without your cooperation.
What if I reported nothing in past years? The tax agency already has the 172 and 173 data. If your IRPF was not filed correctly, you could receive a CR3 notice. Read our article on how the tax agency detects Binance activity too.
3. DAC8: the directive that closes the European net
Modelo 172 and Modelo 173 only cover Spanish exchanges. What about Binance, Kraken, OKX or Coinbase?
That is where the DAC8 directive (Directive on Administrative Cooperation) comes in. From 1 January 2026, every crypto-asset service provider (CASP) operating in the EU is required to report automatically to the AEAT:
- The full tax identity of each Spanish client
- Total volume of purchases and sales in euros
- Balances at year end
- Transfers to external wallets (Ledger, MetaMask, Trezor…)
Which means that even if you use a foreign exchange or move funds to a cold wallet, your activity will end up in the hands of the tax agency. There is a full analysis in our article on DAC8 and the end of crypto anonymity.
Why your full history is needed (not just the last year)
Here comes the part that surprises most people: reporting last year’s transactions is not enough. To produce a correct tax report, we have to reconstruct your activity from the very first day you traded.
The reason is called the FIFO method.
What is the FIFO method and why does it reach back into earlier years?
FIFO stands for First In, First Out. It is the compulsory criterion the AEAT imposes for calculating capital gains and losses on crypto.
When you sell Bitcoin, you are not selling “your Bitcoin” as one homogeneous block. The tax agency assumes you are selling the first Bitcoin you bought, at its original acquisition price.
A worked example:
| Transaction | Date | Amount | Price |
|---|---|---|---|
| Purchase 1 | 2019 | 0.5 BTC | €8,000 |
| Purchase 2 | 2021 | 0.3 BTC | €35,000 |
| Purchase 3 | 2024 | 0.2 BTC | €60,000 |
| Sale | 2025 | 0.4 BTC | €80,000 |
To calculate the gain on that 2025 sale, FIFO requires the price of the 2019 purchase (€8,000) to be used for the first 0.4 BTC sold, not the most recent purchase. The gain works out like this:
- Sale price: €80,000 × 0.4 = €32,000
- FIFO acquisition cost: €8,000 × 0.4 = €3,200
- Capital gain: €28,800
Without the 2019 data you could not apply FIFO correctly and the report would be wrong. The tax agency would assume a cost of zero by default, which sends the taxable base through the roof.
The full walkthrough is in our article on the FIFO method for crypto.
Swaps and cross-platform traceability
It gets more complicated still with swaps (exchanging BTC for ETH, for instance). Every swap is a taxable event: you have to report the gain or loss on the BTC sold and record the ETH bought at its market price at that moment.
If you sell that ETH three years later, FIFO looks back to the day of the swap to establish its cost. Without the full history, that chain breaks.
That is why we always ask for the CSV files from day one, even for transactions from many years ago. It is not red tape: it is the only way to calculate your tax correctly.
Summary: why it has to be reported (and why we need everything)
| Factor | What it means |
|---|---|
| Modelo 172 | The tax agency already knows your balances on Spanish exchanges |
| Modelo 173 | The tax agency already knows your transactions on Spanish exchanges |
| DAC8 (from 2026) | The tax agency will automatically receive data from European exchanges and transfers to external wallets |
| FIFO method | Gains are calculated using the cost of your earliest purchases, which is why the history is needed |
| Swaps | Every crypto-to-crypto exchange creates a cost chain that only makes sense with complete traceability |
Anonymity stopped being an option. And calculating tax correctly demands complete information, not just the last tax year.
Frequently asked questions
If I never reported anything, can I regularise now without a penalty?
Yes. If you file a voluntary amended return before receiving a formal demand from the tax agency, the surcharges are considerably lower. If you wait for an assessment or a notice to land, penalties can run from 50% to 150% of the tax due.
What if I lost the data from years ago?
Most exchanges let you download the full history (Binance, Kraken, Coinbase, Bit2Me, Bitvavo…). We have step-by-step guides for each of them. If a file is missing, we can reconstruct stretches of it from bank statements and on-chain data.
Do I have to report if I have only held and never sold?
Yes, though it is a matter of informing rather than paying: if your crypto holdings on foreign platforms exceed €50,000 as at 31 December, you have to file Modelo 721 even if you never sold a thing. Under IRPF you only report when you sell or swap, but the 721 is an information return.
Are cold wallets still “invisible”?
Not entirely. The tax agency can trace them if you sent funds from an identified exchange. We explain it in detail in how the tax agency knows I have a cold wallet.
What about transactions on exchanges that have since shut down (FTX, Celsius…)?
They count too. We need the CSV files or, failing that, the confirmation emails, screenshots or any record that lets those transactions be reconstructed. Without them, the FIFO chain is broken.
Need help regularising your history?
At colvence we specialise in reconstructing crypto traceability from day one and applying FIFO correctly to complex activity (DeFi, swaps, staking, airdrops). We prepare your profit and loss report ready for your tax return.
Contact us on WhatsApp and we will review your case.
Víctor Lázaro
Tax adviser, colvence.com
