How portfolio rebalancing is calculated
Rebalancing returns a portfolio to its intended allocation after price movements have pulled it away. You set target weights, the market changes them, and rebalancing trades the difference back. The calculation is straightforward: work out the current weight of each holding, compare it against target, and convert the gap into a buy or sell amount.
The uncomfortable part is what that implies. Rebalancing sells whatever has gone up and buys whatever has gone down — by design, not by accident. It is a rule that systematically trims your best performer to fund your worst. That is the entire mechanism, and it is why most people find it hard to actually do.
There are two common triggers. Calendar rebalancing acts at fixed intervals regardless of drift. Threshold rebalancing acts only when a holding drifts beyond a set band. Threshold rules generally trade less in quiet markets and respond faster to genuine moves; calendar rules are simpler to follow and much harder to rationalise your way out of. Either beats the third option, which is deciding each time and calling it judgement.
Worked example
A portfolio targeting 60% BTC, 30% ETH and 10% stablecoins. BTC has rallied, so the actual split has drifted away from target.
| Input | Value |
|---|
| Total value now | 12,000 |
| BTC — value / weight / target | 8,000 / 66.67% / 60% |
| ETH — value / weight / target | 3,000 / 25.00% / 30% |
| Stablecoins — value / weight / target | 1,000 / 8.33% / 10% |
| BTC drift | +6.67 points |
| Rebalancing trades | Sell 800 BTC, buy 600 ETH, buy 200 stables |
| Turnover / fees at 0.20% | 1,600 / 3.20 |
Change only the band and the answer changes completely. Under a 5-point absolute band, BTC breaches and you trade. Under a relative band of 25% of target weight, BTC's tolerated range is 45% to 75% and ETH's is 22.5% to 37.5% — both holdings sit inside, and you do nothing at all. The band, not the drift, decides how often you incur fees and taxable events.
How to use this calculator
- Write down target weights before you need them, and record why you chose each one — the reasoning is what you will want when the market makes you doubt it.
- Enter current values, not purchase prices; drift is measured against what the holdings are worth today.
- Pick a rule — calendar or threshold — and set the band explicitly. An undefined rule becomes 'rebalance when it feels right', which is not a rule.
- Check the trade list against fees and any tax consequence before executing; a small drift is rarely worth a realised disposal.
- Consider directing new contributions to underweight holdings first, which corrects drift without selling anything.
Frequently asked questions
Does rebalancing improve returns?
Not reliably. It controls risk, which is a different objective. In a sustained trend, rebalancing reduces returns because it keeps trimming the asset that keeps rising. Its value shows up when a concentrated position eventually falls hard and your allocation to it was capped rather than compounding unchecked.
How often should I rebalance?
Less often than most people assume. Quarterly or annually is common for calendar rules, and 5 to 10 percentage points is a common absolute band for threshold rules. More frequent rebalancing means more fees and more taxable disposals for progressively smaller corrections.
Is rebalancing a taxable event?
In most jurisdictions selling one crypto asset for another is a disposal, and disposals are generally taxable even when you never touched conventional currency. This can make rebalancing considerably more expensive than the trading fees alone suggest. Confirm the current rules where you are resident before acting.
Can I rebalance without selling?
Often, yes. Direct new deposits into the underweight holdings until the weights correct themselves. This works well when you are still adding to the portfolio regularly, avoids fees and disposals entirely, and is the cheapest form of rebalancing available.
Should stablecoins be part of the target allocation?
If you intend to hold them, yes — otherwise your real allocation is invisible to the calculation. Including a stablecoin target also gives rebalancing somewhere to put proceeds during a rally and something to spend during a decline, which is much of the point.
What if I no longer believe in one of my targets?
Then change the target deliberately and record the reason, rather than quietly not rebalancing. Drifting away from a plan by inaction is how a diversified portfolio turns into a single concentrated bet without anyone ever deciding to make one.
This calculator is an educational tool. Results are estimates based on the inputs you provide and do not constitute financial advice. Verify figures with your bank, broker or a qualified advisor before acting on them.