Investing term
What is Threshold rule?
Rebalance whenever any sleeve drifts more than a set percentage from its target, regardless of how recently you last rebalanced.
A threshold rule rebalances whenever any part of your portfolio drifts more than a set percentage from its target, regardless of the calendar. It responds to actual movement — acting when the portfolio has genuinely shifted, and doing nothing when it hasn't — rather than trading on a fixed schedule.
Compared to a calendar rule, a threshold rule is more responsive: it rebalances promptly after a big market move that has pushed the mix off target, and it avoids unnecessary trades in quiet periods when little has drifted. The trade-off is that it requires monitoring — you have to check whether drift has crossed the threshold — whereas a calendar rule just runs on a date. In practice the two approaches produce similar results for most investors, and many combine them: check on a schedule, but only rebalance if drift has exceeded the threshold, getting the discipline of the calendar with the responsiveness of the threshold.
A threshold rule rebalances only when a holding drifts past a set band from target, regardless of the calendar. Responsive to real moves and quiet when nothing changes — but it needs monitoring.
For example
You set a 5% threshold; your stocks drift from a 60% target to 66%, crossing it, so you rebalance — but in a flat year where nothing drifts past 5%, you leave the portfolio alone.
Learn it by doing
That's Threshold rule in theory — it clicks when you use it. Practise it hands-on in a free, interactive lesson (Stage 18, Rebalancing & Maintenance).
Try the free lesson →Why it matters to you
A threshold rule matters because it ties rebalancing to what actually happens in the portfolio rather than to the calendar, acting when drift is real and staying still when it isn't. That responsiveness controls risk promptly after big moves while avoiding needless trades and tax in quiet times. Understanding the trade-off with calendar rules — responsiveness versus monitoring effort — helps you pick, or combine, the approach you'll actually follow, which matters more than the exact method.
⚠ Setting the threshold too tight
A threshold set too small — rebalancing at tiny deviations — triggers frequent trades that rack up costs and, in a taxable account, tax drag, for little risk benefit. Over-sensitive thresholds turn rebalancing into churn. A modest band that only trips on genuine drift captures the risk-control benefit without the excessive trading, so the threshold should be wide enough to ignore minor, normal fluctuations.