Portfolio rebalancing calculator

Rebalancing does not predict prices. It brings a holding that drifted away from your plan back toward a target chosen before the market moved.

When to act

Choose the target before the market moves. Consider adjusting only when the holding crosses a tolerance band you set in advance or at a scheduled review, rather than using “rebalancing” as a label for chasing prices.

If the target is unclear, read how much to allocate, then use the staged-buy calculator to divide an adjustment.

How this calculator works

Two steps, with nothing hidden:

• Target holding = portfolio value × target allocation
• Adjustment = target holding − current holding (positive means add, negative means reduce)

The portfolio value here is the current one, because rebalancing normally happens inside the portfolio: sell some of what ran up, buy some of what lagged, total unchanged. If you plan to correct the drift with new money instead, add that money to the portfolio value first, then read the target.

What triggers it: calendar or tolerance band

There are really only two rules in common use, and each has a cost:

• Calendar: look every six or twelve months. It is simple, needs no monitoring, and gives you no opening to act on a whim. The cost is the occasional wasted trip when the drift turns out to be trivial.
• Tolerance band: act only when the actual weight has drifted past a margin you set in advance, say five percentage points. You only trade when something has genuinely moved. The cost is that you have to glance at it from time to time.

The practical answer is usually both: check on a schedule, but act only when the band is crossed. Which one you pick matters less than the fact that the rule has to exist before the market moves. Deciding after the fact when a position deserves trimming is not rebalancing.

Rebalancing has a price

The calculator gives you an ideal figure. Executing it costs at least three things:

• Fees and spreads. Every adjustment pays them, and on small amounts they can swallow the benefit entirely.
• Possible tax. Selling a position at a gain triggers capital gains tax in many places, and the rules vary widely. Go by the current official rules where you live.
• Whole units. Many holdings cannot be traded in fractions, so the amount you calculate can usually only be approximated.

That makes a tolerance band a cost control as much as a discipline: it keeps out the small adjustments that change nothing visible while still charging you a fee.

What rebalancing is not

It is often read as a trading technique, which is close to the opposite of what it does:

• Not market timing. It makes no claim about which asset rises next. It only looks at how far the current weights sit from the plan.
• Not a stop-loss. The asset that fell is the one you buy in a rebalance, which is the exact reverse of cutting a loss, and the part people find hardest to actually do.
• Not a way to raise returns. What it controls is risk exposure: it stops one asset quietly growing into most of your portfolio after a good run.

In one line: rebalancing sets a ratio you chose calmly against the way you feel right now. If the target weight is still unclear, read how much to allocate first, settle the ratio, then come back to this tool.

FAQ

What is the rebalancing formula?

Target holding = portfolio value × target allocation; adjustment = target holding − current holding. A positive result means add to the position, a negative one means reduce it. If you intend to correct the drift with new money, add that money to the portfolio value before reading the target.

How often should I rebalance?

There is no standard answer, but either rule beats acting whenever it occurs to you: check every six or twelve months, or act only once the weight has drifted past a margin you set in advance. Combining the two is common. What matters is that the rule exists before the market moves rather than being justified afterwards.

Does rebalancing require selling?

Not necessarily. If you are still adding money regularly, you can direct new contributions to whatever is currently underweight and pull the ratio back by buying more of the smaller side. That avoids the tax and trading costs a sale can trigger, which is especially worthwhile on modest amounts.

Does rebalancing improve returns?

It should not be treated as a way to earn more. What it actually does is control risk exposure, stopping one asset from quietly taking over most of the portfolio after a strong run. In some years it will cost you return, for example by trimming the thing that kept rising. That is the price of controlling risk.