Portfolio drift is the gap between the mix you hold now and the target mix you set. You measure it by comparing each asset class's share of the portfolio with its target share. Markets move prices at different rates, so drift appears even when you change nothing.
Updated October 2026
Suppose you set a target of 50% US stocks and 25% bonds. If stocks rise faster than bonds, stocks become a larger share of the total. You did not buy anything, yet your mix changed. The same happens in reverse after a fall in stocks.
Contributions and withdrawals also cause drift. Money added to one account, or taken from another, shifts the shares unless it matches your targets.
Drift only has meaning against a target. If you have not decided on target percentages, there is nothing to drift from. Targets are your own choice. Nothing in the arithmetic tells you what they should be.
Each answers a different question. Points are easy to compare across classes. Relative drift shows proportional change. Dollars show what it would take to close the gap.
A portfolio is worth $100,000. The targets and current values are below.
| Asset class | Target | Current value | Current share | Drift (points) | Drift (relative) | Drift ($) |
|---|---|---|---|---|---|---|
| US stocks | 50% | $56,000 | 56% | +6 | +12% | +$6,000 |
| International stocks | 20% | $19,000 | 19% | -1 | -5% | -$1,000 |
| Bonds | 25% | $21,000 | 21% | -4 | -16% | -$4,000 |
| Cash | 5% | $4,000 | 4% | -1 | -20% | -$1,000 |
The dollar column sums to zero, because the portfolio total is fixed and any excess in one class is a shortfall elsewhere. US stocks are the largest gap in points and dollars. Cash is the largest gap in relative terms, but on a small base, so $1,000 matters little in dollars.
Which measure to watch is a choice. A rule based on points is simple. A rule based on relative drift suits portfolios with small classes.
Drift depends on the denominator. Decide whether the portfolio is only your brokerage account, or every account including retirement accounts and health savings. A combined total can show a different drift than any single account, which is why many people measure across everything. The next guide in this series covers that.
Be consistent about cash too. Including emergency savings in the portfolio lowers every other share. Excluding it raises them. Either is fine if you use the same definition each time.
Drift changes slowly except in sharp markets. Checking monthly or quarterly is common. Checking daily mostly reports market noise. Some people define a threshold, such as 5 points, and look only when a class crosses it. That is the idea behind a rebalancing band, covered in the rebalancing guide.
Drift says where you are relative to a target. It does not say whether the target is right, whether a position will rise or fall, or whether anything needs to change. Taxes, trading costs and your own timeline all matter to what you do next, and a tax professional or financial adviser can speak to your situation.
Stridefly breaks your portfolio down by asset class and sub-class. You set the targets, and drift shows how far each one has moved from where you set it. The targets are yours; Stridefly does not tell you what they should be. You can scope the view to everything you connect or import, by account owner, or to taxable versus retirement accounts.
Stridefly does not give investment advice, recommend securities or place trades.
Read more on the investing page, or join the waitlist for the private beta.
Portfolio drift is the difference between your current allocation and your target allocation, measured for each asset class.
Subtract the target share from the current share. A 56% share against a 50% target is +6 percentage points, or 12% relative to the target.
Different assets change price at different rates, so their shares of the total move even when you buy and sell nothing.
Monthly or quarterly is common. Some people check only when a class moves past a threshold they have chosen.
Stridefly is in private beta. Join the waitlist and we will email you when a spot opens. Prefer to look around first? Demo mode lets you explore sample data before you connect anything.