Portfolio rebalancing tool: set an index rebalancing schedule, then backtest what it changed
Portfolio rebalancing resets a basket to its target weights instead of letting it drift into something you never designed. Indexes lets you set a rebalancing schedule so your basket resets to its target weights instead of drifting, then backtests the difference. See how quarterly rebalancing changed an AI-infrastructure index versus letting the winners run against the S&P 500.
Educational only · Never places a trade
In short
Portfolio rebalancing is the practice of resetting a portfolio or index back to its target weights on a schedule, because holdings drift as prices move and a basket left alone slowly becomes something you did not design. Indexes is a portfolio rebalancing tool, and an index rebalancing tool, that lets you set a rebalancing schedule, monthly, quarterly, or annually, and then applies it inside the backtest so you can study the effect. You can take an AI-infrastructure index, backtest it with quarterly rebalancing against a version that never rebalances, and see how resetting to target weights changed the hypothetical return and drawdown against the S&P 500. This turns portfolio rebalancing from a rule of thumb into something you can measure. The results are hypothetical historical performance, and past performance does not guarantee future results. Indexes is an informational and educational tool only, it does not constitute investment advice, and it never places a trade, connects to a brokerage, or holds any money. Rebalancing here is a study setting, not an instruction to move real holdings.
What you get
Rebalancing, built for investors and analysts
Set a schedule
Choose monthly, quarterly, or annual rebalancing, so your basket resets to target weights on a cadence you decide instead of drifting.
Keep weights on target
Rebalancing pulls each holding back to its intended weight, so an AI-infrastructure index keeps studying the theme you designed, not the drift.
Backtest the effect
Compare a rebalanced version against a drift version through history, so the impact of a rebalancing schedule is measured rather than assumed.
A study, not an action
Rebalancing is applied inside the backtest only. Indexes never trades or moves holdings, so the schedule is purely for learning.
How it works
From holdings to a tracked index in four steps
Set target weights
Build your index and lock in the weights you want it to hold, so there is a target for rebalancing to reset toward.
Choose a cadence
Pick a rebalancing schedule of monthly, quarterly, or annual, depending on the drift you want to study and control.
Backtest with and without
Replay the basket through history both rebalanced and left to drift, so you can see how the schedule changed the outcome.
Study the impact
Use the comparison to understand rebalancing. Results are hypothetical, past performance is no guarantee, and Indexes never trades.
Questions
Index rebalancing, answered
How does index rebalancing work?
Rebalancing resets an index back to its target weights on a fixed schedule. Prices move, so a holding that started at 20% drifts up or down over the quarter. At each rebalance date the weights are recalculated to the original targets, which trims what grew and tops up what lagged. Rebalancing changes the weights of existing members; reconstitution is the separate step that adds and removes companies. Most large indexes do both, on different cycles.
What are the index rebalancing dates?
The S&P 500 rebalances quarterly, effective after the close on the third Friday of March, June, September and December. The Russell 1000, 2000 and 3000 reconstitute once a year, effective the fourth Friday of June: in 2026 the final reconstitution came after the close on Friday June 26 and the rebuilt indexes opened Monday June 29. The Nasdaq-100 reviews weights quarterly and reconstitutes annually in December, announced around the second Friday and effective after the close on the third. The Dow Jones Industrial Average has no fixed schedule at all, because a committee decides its changes.
How often does QQQ rebalance?
QQQ tracks the Nasdaq-100, so it follows that index rather than setting its own schedule. The Nasdaq-100 runs a quarterly weight review, which caps the largest members when concentration passes defined limits, plus one annual reconstitution each December that changes which companies are in the index. The December reconstitution is announced around the second Friday and takes effect after the close on the third Friday.
How often are index funds rebalanced?
Most major stock indexes reconstitute or rebalance quarterly, with the S&P indexes reviewing on a quarterly cycle. Individual funds tracking them follow that schedule. For a portfolio you run yourself, annual with a drift band is the more common recommendation, since frequent resets add cost without adding much. The detail is in how often index funds are rebalanced.
What is an index rebalancing trading strategy?
It is the practice of trading ahead of a known index change, because index funds are forced to buy added names and sell deleted ones near the effective date regardless of price. That predictability is why reconstitution days such as the June Russell rebalance are among the highest-volume sessions of the year. Index providers have responded by moving to longer announcement windows and phased implementation, which has compressed the effect considerably. It is a professional strategy that depends on execution and cost control, not something a schedule setting in a backtest replicates, and nothing here is a recommendation to attempt it.
What is the best rebalancing frequency?
For most portfolios, annual rebalancing plus a tolerance band beats a fixed monthly schedule. Monthly resets react to noise and, in a taxable US account, realize gains you did not need to realize. Our guide to rebalancing frequency works through the tradeoff.
What is automatic portfolio rebalancing?
It is a setting that resets your holdings to their target weights on a fixed cadence without you approving each trade. Robo-advisors and most 401(k) providers offer it, usually quarterly or annually, and some rebalance on drift bands instead of a calendar. The tradeoff is that automatic rebalancing in a taxable account realizes gains you did not choose to realize, which is why the automatic option is far more attractive inside an IRA or a 401(k) than in a brokerage account.
Does rebalancing trigger capital gains tax?
In a taxable brokerage account, yes. Selling the holdings that grew realizes a gain, and if you held them less than a year that gain is taxed at ordinary rates rather than the 0/15/20 long-term rates. Inside an IRA or 401(k) it costs nothing. Before setting a frequent schedule on a taxable account, work out the bill with a capital gains tax calculator, and consider rebalancing with new contributions instead of sales.
What is the 5/25 rule for rebalancing?
A drift band rule: rebalance a holding when it moves more than 5 percentage points from its target in absolute terms, or more than 25% of its target weight in relative terms, whichever is smaller. A 40% target triggers at 5 points, while a 4% target triggers at 1 point.
Does rebalancing improve returns?
Not reliably. Rebalancing is primarily a risk control that keeps a portfolio from drifting into a concentration you never chose. It can add return when assets mean-revert and cost return in a long trend, which is why testing it against a drift version over real history is more useful than assuming either way.
Can I test a rebalancing strategy before using it?
Yes, and it is the point of doing this here. Build the index, set a schedule, and backtest the rebalanced version against one left to drift over the same dates. Results are hypothetical historical performance and Indexes never places a trade.
More features
Build your index and see how it backtests
Bundle stocks or crypto into your own weighted index, backtest it against real market history, and track it against the S&P 500 or BTC. No brokerage account and no spreadsheets. Indexes is educational and informational only, and it never places a trade.