Investing term
What is Drift?
The gradual shift in your portfolio's mix as some assets grow faster than others.
Drift is the gradual shift in your portfolio's mix as faster-growing holdings swell their share and slower ones shrink. You don't have to do anything for it to happen — a strong run in stocks quietly raises their weight, and with it the overall risk of the portfolio.
Because it's automatic and invisible, drift tends to push your risk higher than you intended, exactly when markets have run up and a correction is more likely. The portfolio you end up holding is riskier than the one you designed, simply because the winners now dominate. Rebalancing is the deliberate act of undoing drift — selling a little of what's grown most to top up what's lagged, restoring the mix you chose.
Left alone through a strong year, a 60/40 mix drifts toward 68/32 — quietly taking on more risk than you chose. Rebalancing is the deliberate act of undoing that drift.
For example
Left alone through a strong stock year, a 60/40 portfolio can drift to 68/32 — quietly taking on more risk than you signed up for, without a single trade.
Learn it by doing
That's Drift in theory — it clicks when you use it. Practise it hands-on in a free, interactive lesson (Stage 10, Building Your First Portfolio).
Try the free lesson →Why it matters to you
Drift matters because it silently changes your risk level without your consent, usually raising it right when caution would serve you best. The mix you carefully chose slowly becomes something more aggressive, so a downturn hits harder than you planned for. Recognising that a portfolio left alone doesn't stay put — it drifts toward risk — is what makes periodic rebalancing feel necessary rather than optional.
⚠ Mistaking drift for good performance
When your best holdings grow and dominate, it feels like success — so leaving the drifted mix alone seems natural. But that's an accidental increase in risk, not a decision. The portfolio is now more exposed to a fall in those winners than you intended. Correct drift on a rule, rather than admiring it as performance.