Portfolio Rebalancing Calculator
Last updated: 27 June 2026
Reviewed by Gavin Meiring, Lead research and primary author · Doctoral Candidate (Corporate Governance) · Research and drafting assisted by AI
- Rebalancing forces you to do the hardest thing in investing on a schedule: sell what has gone up and buy what has gone down — a mechanical version of 'buy low, sell high'.
- Most advisors use threshold-based rebalancing, acting when an asset drifts more than a set amount (often 5 percentage points) from its target — because constant tinkering just racks up trading costs.
- In mean-reverting markets rebalancing can earn a 'rebalancing bonus', but the effect reverses in trending markets where letting winners run does better — which is why the strategy is really about risk control, not extra return.
Portfolio Rebalancing Calculator
A portfolio rebalancing calculator shows you how far your current asset allocation has drifted from your target and tells you exactly how much to buy or sell in each asset class to restore balance. It is used by investors who maintain a strategic asset allocation and need to periodically realign their portfolio after market movements.
How to Use the Portfolio Rebalancing Calculator
- Enter your target allocation as a percentage for each asset class, for example 60% equities, 30% bonds, 10% cash.
- Enter the current market value of each holding.
- The calculator computes the current percentage weight of each asset class.
- It then compares current weights to target weights and calculates the pound difference for each.
- The output shows how much to buy or sell in each asset class to return to the target allocation.
The Formula
Current Weight (%) = (Current Value of Asset / Total Portfolio Value) x 100
Drift = Current Weight - Target Weight
Rebalancing Trade = Total Portfolio Value x (Target Weight - Current Weight) / 100
A positive rebalancing trade means buying that asset class. A negative trade means selling. The total of all rebalancing trades nets to zero, as you are redistributing within the existing portfolio value.
Real-World Example
Your portfolio has a target allocation of 70% equities and 30% bonds. You started with £100,000. After a strong equity market, your portfolio is now worth £115,000: equities have grown to £87,000 and bonds to £28,000.
Current weights: equities = £87,000 / £115,000 = 75.7%. Bonds = £28,000 / £115,000 = 24.3%.
Target values at £115,000: equities = £80,500, bonds = £34,500.
Rebalancing trades: sell £6,500 of equities (£87,000 - £80,500), buy £6,500 of bonds (£34,500 - £28,000).
After trading, you are back at 70/30, locking in some of the equity gains and restoring your intended risk profile.
When and How Often to Rebalance
There are two main rebalancing triggers. Calendar-based rebalancing happens at fixed intervals, typically quarterly or annually, regardless of drift. Threshold-based rebalancing happens when any asset class drifts beyond a set tolerance, commonly 5% above or below target. Research suggests that threshold-based rebalancing is slightly more efficient, as it responds to actual drift rather than a fixed schedule. In practice, many investors combine both approaches: they review the portfolio quarterly and rebalance if any allocation has moved more than 5% from target. In tax-sheltered accounts such as ISAs and SIPPs, rebalancing has no immediate tax cost, making it simpler. In taxable accounts, the tax implications of selling gains must be weighed against the cost of maintaining a misaligned portfolio.
Frequently Asked Questions
How often should I rebalance my portfolio? Annual rebalancing is sufficient for most long-term investors and keeps transaction costs low. More frequent rebalancing may be warranted in highly volatile markets or if your portfolio has drifted significantly from targets.
Does rebalancing improve returns? Rebalancing primarily controls risk by preventing any one asset class from dominating the portfolio. It can modestly improve risk-adjusted returns by systematically selling outperforming assets and buying underperforming ones. However, in strong trending markets, rebalancing can slightly reduce absolute returns.
Should I rebalance by buying or selling? If you are still contributing regularly, directing new contributions to underweight assets is the most tax-efficient way to rebalance, as you avoid selling assets and triggering capital gains. Selling and buying is necessary when contributions alone cannot restore the target allocation.
What is an acceptable drift tolerance? Most investment professionals suggest a tolerance band of 5% around each target weight. Some investors use tighter bands of 3% for more precise control, though this increases transaction frequency and costs.
Should I rebalance inside a tax-sheltered account first?
Yes, where you have the choice. Selling inside an ISA or SIPP does not trigger capital gains tax, so the trade costs the dealing charge and nothing else. Keeping the taxable account balanced with new contributions and the sheltered account balanced with trades holds the tax bill down. Plug your own figures into the calculator above.
How do I rebalance a portfolio spread across several accounts?
Treat the accounts as one portfolio for the target weights, then decide where each trade lands. Add each sleeve across all accounts, compare the total with the target, and place the trades in the accounts where they cost least to execute. The calculator above works on the combined values.
Does rebalancing change my total portfolio value?
No. The trades move money between sleeves, and the total stays put apart from the dealing costs. What changes is the risk. A portfolio that drifts to 69% equities carries more equity risk than the 60% you chose, whether or not the value moved.
Worked example: a three-asset portfolio at £250,000
A portfolio holds £172,400 in equities, £61,800 in bonds, and £15,800 in cash, for a total of £250,000. The target is 60% equities, 30% bonds, and 10% cash, and a strong run in equities has pushed the first sleeve well past its target.
| Sleeve | Value | Current weight | Target weight | Drift | Target value | Trade |
|---|---|---|---|---|---|---|
| Equities | £172,400 | 68.96% | 60% | +8.96 points | £150,000 | Sell £22,400 |
| Bonds | £61,800 | 24.72% | 30% | -5.28 points | £75,000 | Buy £13,200 |
| Cash | £15,800 | 6.32% | 10% | -3.68 points | £25,000 | Buy £9,200 |
| Total | £250,000 | 100% | 100% | 0 | £250,000 | £0 net |
The three trades add to zero because rebalancing moves money inside the portfolio. Nothing is added and nothing is withdrawn. The equity sleeve gave up 8.96 points of weight, and that is where the bond and cash purchases came from.
What a tolerance band looks like in pounds
A band only becomes actionable once you convert the percentages into values. On £250,000 with a 60% equity target:
| Band | Equity weight range | Equity value range | Position today |
|---|---|---|---|
| 3 points | 57% to 63% | £142,500 to £157,500 | £14,900 above the top |
| 5 points | 55% to 65% | £137,500 to £162,500 | £9,900 above the top |
| 7 points | 53% to 67% | £132,500 to £167,500 | £4,900 above the top |
At £172,400 the equity sleeve sits outside all three bands, so any of them triggers a trade. A portfolio holding £160,000 of equities would sit inside the 5 point band at a drift of four points and no trade would be needed. That is the point of a band: it lets small drift alone and spends the dealing cost only when the misalignment is worth correcting.
Costs of trading and the case for a threshold
Every trade carries a cost. Selling £22,400 of equities at a 0.5% dealing charge costs £112, and a 1% round trip on the same amount costs £224. Those figures look small next to the £22,400 being repositioned, but they repeat. A portfolio rebalanced every quarter pays them four times a year whether or not the drift justified the trade, and a taxable account also realises capital gains on whatever it sells. A tolerance band pays the cost only when the misalignment is large enough to act on, which is the practical argument for measuring drift before trading rather than trading on a fixed date.
Contributions avoid the sale altogether. Directing new money to the underweight sleeves closes the gap while the contributions are large enough. On the £13,200 bond shortfall above, a monthly contribution of £1,100 closes it inside twelve months with nothing sold.
Rebalancing with contributions instead of trades
New contributions can close a gap without a single sale. On the £250,000 portfolio above, bonds are £13,200 short of target and cash is £9,200 short.
| Approach | Monthly routing | Bond gap closed after | Cash gap closed after |
|---|---|---|---|
| Direct the money to the shortfalls | £1,100 to bonds, then £1,100 to cash | 12 months | 20.4 months |
| Split the money in target proportions | £330 bonds, £660 equities, £110 cash | never closes | never closes |
The second row is the trap. Routing contributions in the target proportions holds the current weights exactly where they are, so the 8.96 point equity overweight persists for as long as the portfolio stays unbalanced. That is not rebalancing, and the portfolio keeps carrying more equity risk than the target allows. The contribution route also assumes fresh money is arriving at £1,100 a month. A portfolio in drawdown has no such lever, and the trade is the only option.
One ordering rule helps. Use the sheltered account for the trade, because the sale there costs nothing in tax, and use the taxable account for the contributions, because money added to the underweight sleeve raises its cost base instead of realising a gain.
Drift measured against the target or against the sleeve
A five point band is five points of the whole portfolio, so it means different things to different sleeves. On a 60% equity target the band runs from 55% to 65%, a range of 10 points. On a 30% bond target the same five point band runs from 25% to 35%, which is a wider swing in proportional terms. Some investors use a proportional rule instead and trade when a sleeve moves 25% away from its own target. On a 30% bond target that is 22.5% to 37.5%. The choice changes how often you trade, so pick one rule and keep it.
Sources
- Investor.gov, US Securities and Exchange Commission, Rebalancing glossary entry. https://www.investor.gov/introduction-investing/investing-basics/glossary/rebalancing. Accessed 2026-09-13.
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