Risk and diversification of your DEGIRO portfolio: beta and volatility explained

Beta measures how strongly your portfolio moves with a market index such as the S&P 500 (a beta of 1.0 means it moves exactly as much as the market), while volatility measures the spread of your own returns around your own average — so two portfolios with the same average return can still have a completely different risk profile.

Return is only half the story

Two portfolios can show exactly the same average return over five years, yet feel completely different: one moves calmly with the market, the other swings wildly up and down. Anyone looking only at return misses that side of the story entirely. Return is visible. Risk isn’t — until it goes wrong. Two metrics do capture that risk: beta and volatility.

Beta: how sensitive is your portfolio to the market?

Beta measures how strongly your portfolio moves with a broad market index (such as the S&P 500 or MSCI World). A beta of 1.0 means: your portfolio moves, on average, exactly as much as the market.

• Beta > 1 — your portfolio amplifies market movements. With a beta of 1.2, a 10% market rise would correspond to an expected rise of roughly 12% in your portfolio — but the same applies to your disadvantage on a decline.
• Beta < 1 — your portfolio dampens market movements. With a beta of 0.6, that same 10% market rise would correspond to an expected rise of roughly 6%.

So beta says nothing about whether your return is good or bad, but it does say how much that return could swing if the market moves. Whether you add anything on top of that market sensitivity is measured by alpha; see alpha, beta and R² of your portfolio.

Volatility: how bumpy is the ride itself?

Does a portfolio feel bumpy, or actually is it? Where beta compares your portfolio to the market, volatility measures the spread of your own returns relative to your own average — usually expressed as the standard deviation of monthly returns. High volatility means large swings in both directions, even if the average return over the whole period is identical to a calmer portfolio.

This is why a distribution of monthly returns (a histogram against a normal curve) is so useful: two portfolios with the same average can look completely different once you factor in the spread — one tightly clustered around the average, the other with fat tails of exceptionally good and bad months.

What’s normal volatility for a stock portfolio?

A broad stock portfolio typically has annual volatility of 15-20%; well above 25% it starts to get unusually turbulent. A similar rule of thumb applies to beta: a beta between 0.8 and 1.2 is normal for a diversified stock portfolio, while a beta above 1.5 usually points to a concentrated position in volatile growth stocks.

Why diversification affects this

Spreading across different asset classes, sectors and regions is the primary tool for taming volatility without necessarily sacrificing return: movements that don’t move in perfect lockstep partly cancel each other out. To know whether you’re actually diversified, you have to look beyond the number of positions — two tech stocks and a tech ETF feel like diversification, but in practice move largely together: a correlation of 0.85 to 0.95 between a stock like that, a sector ETF and a broad tech tracker is not unusual. That ties in with what we see under ETF overlap and concentration: the same underlying risk often comes back through several positions at once.

The uncomfortable part is that correlations between asset classes often creep toward 1 during a crash — diversification works least well at exactly the moment you need it most. That’s also precisely why a deep drawdown so often seems to hit every position at once, including ones that on paper had little to do with each other. Once you know where you’re overweight, portfolio rebalancing brings you back to your target allocation.

How ClearAnalyser calculates this for you

ClearAnalyser calculates your portfolio’s beta and volatility live, visualises your return distribution against a normal curve, and categorises your holdings across five dimensions (asset class, sector, geography, style and market cap) to show whether your diversification is actually diversification. How other tools handle risk figures is shown in the DEGIRO portfolio tracker comparison.

Sources: Beta — Investopedia · Volatility — Investopedia