---
title: "Portfolio Drift Calculator: Rebalance Band Check | RupeeCase"
description: "Portfolio drift calculator: how far a holding has drifted from its target weight, whether a band rule says rebalance, and the trade and fee to restore it."
source_url: "https://www.rupeecase.com/learn/tools/drift-threshold-calculator"
---

Weight now**23.6%**
Drift from the target**3.6%**percentage points
Against a 5 point band**Inside: no trade under this rule**
Traded to restore the target**₹80,000**sell plus buy
RupeeCase fee on that trade**₹160**

Weight now = target x (1 + its return) / portfolio growth. The fee is 0.2% of the traded value.
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  01How it works

## In plain words.
After returns, the holding’s weight is its grown value over the grown portfolio. The drift is the gap to the target. A band rule trades only when the drift is larger than the band; the trade sells the excess and buys the rest of the portfolio, so the traded value counts both sides.

    The formula

`Weight now = w(1 + ra) / (w(1 + ra) + (1 - w)(1 + rr))``Drift = weight now - target``Traded value = 2 x |drift| x portfolio value now`

  02Worked example

## The default numbers, by hand.
A 20% holding up 30% while the rest rose 5%: its weight is 23.6%, a drift of 3.6 points, inside a 5 point band. At 40% it would be 25.0%, exactly on the band edge; at 60%, 27.6%, outside.

| Input | Value |
| --- | --- |
| Target weight | 20% |
| Its return since the last rebalance | 30% |
| Rest of the portfolio, return | 5% |
| Band, in percentage points | 5% |
| Portfolio value at the last rebalance | ₹10,00,000 |

| Result | Value |
| --- | --- |
| Weight now | 23.6% |
| Drift from the target | 3.6% |
| Against a 5 point band | Inside: no trade under this rule |
| Traded to restore the target | ₹80,000 |
| RupeeCase fee on that trade | ₹160 |

  03Key concepts

## What to know before you use it.

### Calendar or band
Calendar rebalancing trades on fixed dates; band rebalancing trades when weights move far enough. Many systematic strategies combine both.

### Absolute or relative bands
This calculator uses an absolute band in percentage points. A relative band (for example 25% of the target) widens with the target weight.

### Good to know

* Narrow bands trade more often; wide bands let risk drift further.
* The rebalance cost calculator puts a yearly number on a cadence.

  04Assumptions

## What the calculator assumes.

* One holding against the rest of the portfolio; no cash flows.
* RupeeCase fee of 0.2% of traded value; taxes on gains not included.

  05Questions

## Asked about the Drift and rebalance band.
When should a portfolio be rebalanced?Rules differ: on fixed dates, when a weight leaves a band, or both. The rule matters less than following it consistently.

What is portfolio drift?The gap between a holding’s current weight and its target, caused by different returns since the last rebalance.

    Explore next

## Learn the idea behind the numbers.

* [Blog noteAllocation drift: the risk you didn't choosePortfolio construction, a short note](/blog/2026-07-13-morning-allocation-drift/)
* [Blog noteLast year's best factor is a bad forecastFactors, a short note](/blog/2026-06-17-morning-factor-chasing/)
* [Free module 4.3Rebalancing Strategies9 min read](/learn/path-4/module-4-3-rebalancing-strategies)
* [Free module 10.5Portfolio Monitoring & Rebalancing in Practice9 min read](/learn/path-10/module-10-5-portfolio-monitoring-and-rebalancing-in-practice)
* [StrategyAllcap Multi Asset strategyNifty Total Market, 52 stocks, every 2 weeks](/strategies/allcap-multi-asset)
* [CalculatorRebalance cost at 0.2%Free, with the formula and a worked example](/learn/tools/rebalance-cost-calculator)

      Community

## Join my WhatsApp group.

      Scan the code, fillFill one short form, and join my WhatsApp group. Slides, sources, factsheets and the rebalance logs live there, and members join a daily Google Meet with me.

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06Keep going

## Learn the idea, see it applied.

  [Module 4.3Rebalancing Strategies9 min read, Path 04](/learn/path-4/module-4-3-rebalancing-strategies)[Module 10.5Portfolio Monitoring & Rebalancing in Practice9 min read, Path 10](/learn/path-10/module-10-5-portfolio-monitoring-and-rebalancing-in-practice)[The matching indexAllcap Multi Asset50 stocks, 10% debt, 10% gold. The broad-market engine with a cushion.CAGR40.5%Sharpe1.81Max DD−21.3%Model, back tested, as of 27 Apr 2026. Not client returns, not a promise. Risk band: Moderate.](/strategies/allcap-multi-asset)

  More rebalancing and allocation calculators

[Rebalance cost at 0.2%](/learn/tools/rebalance-cost-calculator)[Asset allocation by risk profile](/learn/tools/asset-allocation-calculator)[All 25 calculators](/learn/tools)

  Education only, not investment advice. RupeeCase is a technology platform operated by QC Alpha Technologies Pvt Ltd; it is not a fund, a PMS or a SEBI registered investment adviser. Model returns are back tested and not a promise of future returns. Figures carry the date they were checked.