How to Diversify a Portfolio
Diversifying does not simply mean owning many investments. It means combining assets that do not all react the same way to the same events. But there is another important condition: the portfolio also has to suit your goals and be comfortable enough to hold on to when markets fall.
Diversification is one of the best-known principles of investing, but also one of the most misunderstood.
Owning ten different assets does not necessarily mean having a diversified portfolio. If they are all exposed to the same risks and react to the market in the same way, the extra protection may be limited.
What matters is understanding how the different assets relate to one another.
Diversifying is combining different risks
A diversified portfolio seeks to combine assets that behave differently.
This is where correlation comes in: a measure of how closely two investments tend to move in the same direction.
The four equity indices from other regions moved closely with global equities (correlation between 0.66 and 0.98). Bonds and gold behaved very differently. Correlation runs from −1 to 1: close to 1, the two almost always rise and fall together; close to 0, they move independently of each other. Monthly returns. MSCI (net, EUR), Bloomberg and iBoxx indices in euros, gold in euros. Source: PortfolYou, from index data. Past performance does not guarantee future results.
When assets that behave differently are combined, losses in one part of the portfolio can be partly offset by the behaviour of others.
This is one of the reasons why portfolios are usually built across different asset classes, regions, sectors and sources of risk, instead of relying on a small number of similar positions.
Diversification does not eliminate losses. The aim is to make the portfolio less dependent on a single market, asset or scenario.
10,000 € invested at the start of 2010, rebalanced monthly, until 29/12/2025. The all-equity portfolio ended with 62,374 € and the 60/40 portfolio with 34,475 €, but in the worst fall (March 2020) the first lost as much as 33.8% and the second 21.9%. In 2022, when equities and bonds fell at the same time, the gap was smaller (16.9% against 14.4%). Equities: MSCI World (net, EUR). Bonds: Bloomberg Global Aggregate (EUR hedged). Source: PortfolYou, based on index data. Past performance does not guarantee future results.
A good portfolio does not exist only on paper
Financial theory teaches how to build portfolios that seek the most efficient combination of expected return and risk.
That logic remains essential. The relationship between assets, volatility and expected return helps explain how different combinations can change the overall risk of a portfolio.
But there is a second dimension that cannot be ignored: investor behaviour.
A theoretically efficient portfolio stops being useful if the investor cannot hold on to it when markets fall.
In practice, some behaviours can undermine a well-built strategy:
- Inertia. Keeping the same allocation for years, even when goals or financial circumstances change.
- Naive diversification. Spreading money across several investments without checking whether they represent genuinely different risks.
- Familiarity. Concentrating too much wealth in the country, sector or company you know best (so-called home bias), mistaking familiarity for lower risk.
- Chasing recent performance. Increasing exposure to the assets that have risen most recently, assuming that performance will continue.
Listed shares held directly by the households of each country: the part in domestic companies, next to that country's weight in the world equity market. In Q4 2025, Portuguese households held 44.9% of these shares in Portuguese companies, in a market that weighs 0.04% of the world. Only shares bought directly count: investment funds are left out and, for Portuguese households, are worth about 4 times as much. Includes non-profit institutions serving households. Sources: ECB, securities holdings statistics by sector (Q4 2025); MSCI ACWI IMI (30/06/2026). PortfolYou calculation.
The problem is not only choosing a suitable portfolio. It is also being able to stick with it when doing so is hard.
Organising the portfolio around goals
One way to bring a financial strategy closer to the investor’s reality is to organise wealth according to the different goals.
Not all money has the same purpose or the same horizon.
An emergency fund may need high liquidity and low risk. Money set aside for a house deposit in a few years may call for more stability. Capital meant for retirement several decades from now may be able to take on more volatility.
This approach links each part of the portfolio to three elements:
- a goal;
- a time horizon;
- a suitable level of risk.
Instead of asking only “what is the portfolio’s volatility?”, another question starts to matter as well:
What is the probability that this money will not be available when it is needed?
This way of thinking helps turn an abstract portfolio into a structure directly tied to the investor’s goals.
Mathematics and behaviour can work together
Building a portfolio does not require choosing between financial diversification and goals-based investing.
The two approaches can complement each other.
Goals help define how much risk each part of your wealth can take. Within each of those needs, the principles of diversification still help in choosing more efficient combinations of assets.
At PortfolYou, Asset Allocation helps turn your profile and goals into a split across asset classes. Portfolio Optimization then lets you analyse different combinations of risk and return within the portfolio.
The right portfolio is not simply the one with the best combination in a formula. It is the one that serves your goals, respects your risk tolerance and can be held on to when markets go through difficult periods.
Adapted from “Diversificação: da carteira tradicional para a carteira modificada”, originally published on the Future Proof blog.