Bitcoin has been around for more than fifteen years. In that time, an investor who bought in January 2015 and held through to 2025 would have multiplied their money by more than a hundredfold. That sentence circulates widely in forums, on social media, and in conversation. What circulates less: who actually held on through the 80% drawdowns that occurred during that same period, and how many people sold at the worst possible moment. Cryptocurrencies are a real asset class, with real historical returns and real risks. The interesting debate is not whether they exist or whether they matter — it is whether they belong in a personal portfolio and under what conditions.
The appeal and the cost of the crypto promise
The most common argument for including cryptocurrencies in a portfolio is return asymmetry: if a small allocation rises by 1,000%, the positive impact can be very significant, while a 100% loss is limited in absolute terms. This reasoning has a certain mathematical logic, but it overlooks several factors.
The first is correlation during periods of stress. During the episodes of financial stress in 2020 and 2022, cryptocurrencies did not behave as safe-haven assets or genuine diversifiers: they fell alongside equities, in many cases by more. The correlation between Bitcoin and the stock market, which was historically low, has increased significantly in recent years — precisely at the moments when a low correlation would matter most.
The second is the cost of the narrative. The crypto universe has generated more stories of rapid wealth creation than almost any other asset class in history. This attracts many investors at moments of euphoria and drives them out at moments of panic, which means the actual return obtained by the average investor is systematically below the theoretical return of the asset. Studies of actual investor behaviour in Bitcoin show that most people bought during upswings and sold during downswings, earning returns well below the index.
The third is regulatory uncertainty. Unlike equities or bonds, cryptocurrencies do not have a consolidated regulatory framework at the global level. Regulatory changes can dramatically affect their liquidity, taxation, and accessibility.
Real volatility: the data that rarely gets mentioned
The annualised volatility of Bitcoin over the past decade has been between 60% and 80%, depending on the period. For comparison, global equities have an annualised volatility of between 12% and 18%. This means that a portfolio with 5% in Bitcoin adds to that 5% a volatility several times higher than that of a typical equity.
The most significant historical drawdowns in Bitcoin are part of the record. Between December 2017 and December 2018, Bitcoin lost more than 80% of its value. Between November 2021 and November 2022, it fell by more than 75% again. For an asset entered with expectations of high gains, maintaining the position through a decline of that magnitude requires a psychological resilience that few investors actually possess.
Smaller cryptocurrencies — altcoins — show even more extreme volatility. Many have lost 95% or more of their value and never recovered. The idea that “everything that falls will rise again” is not an axiom in this market: there are projects that have simply ceased to exist.
Volatility also has a directly relevant tax dimension. In Spain, gains and losses derived from cryptocurrencies are included in the savings tax base. Every sale, exchange, or use to pay for goods generates a taxable event, which enormously complicates the fiscal management of an active portfolio in this market.
What they actually contribute to a diversified portfolio
Markowitz’s portfolio theory holds that adding a high-volatility but low-correlation asset can improve the efficiency of a portfolio — higher expected return per unit of risk. For years, this was the academic justification for including small positions in Bitcoin.
The problem, as noted above, is that the correlation between Bitcoin and equities has increased significantly since 2020. In recent periods, Bitcoin has behaved more like a risk asset than an uncorrelated one, which reduces its value as a diversifier.
Some studies show that adding between 1% and 5% of Bitcoin to a global equity portfolio would have improved its risk-adjusted return during certain historical periods. Other studies show that this improvement disappears when different periods are considered or when actual investor behaviour is taken into account. There is no clear academic consensus.
What does seem reasonable to conclude is that the diversification potential of cryptocurrencies is more limited than initially presented, and that the historical return improvement is largely explained by the initial adoption period — which is, by definition, unrepeatable.
If you decide to include them: how much and under what conditions
If, after considering all of the above, you decide to include cryptocurrencies in your portfolio, there are some principles that can reduce the most costly mistakes.
Position size. Most financial advisers who consider this possibility limit it to between 1% and 5% of the total portfolio. Above that percentage, the volatility of cryptocurrencies begins to dominate the behaviour of the portfolio as a whole. This is not a universal rule but a reference point for calibrating exposure.
Choice of asset. Within the crypto universe, Bitcoin and Ethereum concentrate the greatest liquidity, the greatest institutional following, and the longest track record. Investing in smaller projects multiplies the risk without guaranteeing higher expected returns.
Custody method. Cryptocurrencies can be held on centralised exchanges or in personal wallets. Centralised exchanges are more convenient but involve counterparty risk — the exchange may fail or be hacked, as has happened several times historically. Holding in a personal wallet requires managing private keys with absolute care: losing them means permanently losing access to the funds.
Taxation. Before trading, it is worth understanding your tax obligations: reporting gains and losses in your annual income tax return, and filing Model 721 if assets are held on foreign exchanges and their value exceeds 50,000 euros.
Time horizon and tolerance. Investing in cryptocurrencies with money you may need within three years, or that you cannot afford to lose, is a particularly dangerous combination given the historical volatility record.
What distinguishes the crypto investor who survives
Most losses in cryptocurrencies do not come from choosing the wrong asset but from three behavioural errors: entering at moments of media euphoria, investing more than can be lost calmly, and selling at the lowest point of the cycle.
The investor who has achieved positive results in this market over several years tends to share certain characteristics: they entered with a small, pre-defined position; they established a clear rule about when to sell or rebalance; and they did not allow the crypto position to dominate their everyday financial decisions.
Cryptocurrencies are an asset class with unique characteristics: high volatility, potential for extreme returns in bull cycles, and the risk of total loss in individual projects. Including them in a portfolio is neither automatically a mistake nor an obligation. It is a decision best made from analysis rather than from social pressure, fear of missing out, or the expectation of getting rich quickly. None of those motivations has historically proven a sound basis for an investment decision.
