Key takeaways
- Drift = actual weight − target weight per class, in percentage points.
- Unequal growth causes it without any action — arithmetic, not error.
- Calendar reviews, threshold bands, and contribution steering are the common responses — all policies, none rules.
What drift measures
For each asset class, drift is actual weight − target weight, in percentage points. A class targeted at 60% sitting at 66% has drifted +6pp. The headline number most tools quote — including this one — is the largest absolute gap across classes: the single furthest departure from your own plan.
Example · drift in dollars
A $50,000 portfolio targeted 60/25/10/5 holds $33,000 in US stocks — 66%, a drift of +6pp. In dollars: 60% of $50,000 is $30,000, so the class sits $3,000 above your own target. Percentage points name the gap; dollars size it.
Why it happens without you
Unequal growth is the whole mechanism. If stocks return 20% while bonds return 2%, a 60/40 becomes roughly 64/36 in one year with no action taken. Drift is not a mistake; it is the arithmetic consequence of holding things that perform differently — which is the point of holding different things.
Does it matter?
Drift changes the risk you carry, not necessarily the return you get. A stock-heavy drift means deeper drawdowns than the plan contemplated; a cash-heavy drift means quieter nights and slower compounding. Whether either is a problem depends entirely on why you chose the original target — drift is a fact, not an alarm.
The common responses
People respond three ways: calendar rebalancing (review on a schedule), threshold bands (act only past a set drift), or contribution steering (aim new money at the underweight classes so the gap closes without selling). All are conventions with trade-offs — the drift number simply tells you where you stand while you decide.
↑ Back to topOpen the Portfolio tracker. Set targets per class and the drift math — points and dollars — runs continuously on your entries.
Open in Capital Allocation →