# Portfolio turnover

Portfolio turnover is the value of securities replaced through trading during a period, commonly measured as the lesser of purchases or sales divided by average portfolio value.

## What it means

A portfolio can change substantially even when its ending value looks much like its starting value. Portfolio turnover measures how much of its holdings were replaced through purchases and sales over a stated period, usually a year. It describes trading activity, not whether the trades were profitable.

The figure is generally expressed as a percentage of average portfolio value. A 25% annual turnover rate means the value counted as replaced during the year equals one-quarter of the portfolio’s average value. It does not mean that every holding changed, or that exactly 25% of the shares were sold.

Portfolio turnover differs from a stock’s **turnover**, which describes trading in that stock relative to its shares or volume. It also differs from changes in portfolio value caused solely by market prices.

## How it is calculated

One common convention is:

`Portfolio turnover (%) = min(total purchases, total sales) / average portfolio value × 100`

- **Total purchases** is the monetary value of securities bought during the period, in US$.
- **Total sales** is the monetary value of securities sold during the same period, in US$.
- **min** selects the smaller of those two amounts, in US$. Using the smaller side helps avoid counting both sides of a replacement trade.
- **Average portfolio value** is the average market value of the portfolio over the period, in US$. The averaging method and treatment of cash can vary by reporting convention.
- **Portfolio turnover** is a percentage for the specified period; a monthly figure is not directly comparable with an annual figure.

Definitions vary. Some calculations adjust for investor contributions and withdrawals or exclude particular short-term instruments. When comparing published rates, check each source’s method and time period.

## Worked example

Suppose a hypothetical stock portfolio has an average value of **US$100,000** during one year. Its trades total **US$30,000 in purchases** and **US$20,000 in sales**.

1. Take the smaller trading total: `min(US$30,000, US$20,000) = US$20,000`.
2. Divide by average portfolio value: `US$20,000 / US$100,000 = 0.20`.
3. Convert to a percentage: `0.20 × 100 = 20%` annual portfolio turnover.

The extra US$10,000 in purchases is not counted under this convention. It might reflect money added to the portfolio; the trading totals alone do not establish why purchases exceeded sales. The 20% rate also does not tell us how many orders were placed or what they cost.

## Why it matters before you trade

Trading can incur commissions, bid-ask spread costs and market impact. More turnover can create more opportunities for these costs, but turnover alone cannot determine the bill: order size, liquidity, execution and the number of trades matter. Tax consequences may also differ by account, holding period and jurisdiction.

Before changing holdings, it can help to distinguish a deliberate rebalance from trading caused by short-term reactions. Estimate the costs of the **proposed** orders rather than applying a fixed cost percentage to historical turnover. A portfolio’s past turnover provides context, while the next basket’s quantities and execution conditions determine the immediate pre-trade questions.

A low rate is not automatically desirable, and a high rate is not automatically a problem. Neither number measures diversification, risk or investment results by itself.

## How PreTrAIde uses it

PreTrAIde does **not** list portfolio turnover as a calculated metric in its product facts. Its pre-trade analysis instead examines a user-built stock basket before an order is placed. For each stock and the basket, it returns a GO, NO-GO or MODIFY verdict with a model-estimated success probability, risk assessment, suggested execution strategy and plain-language reasoning. These verdicts are decision support, not recommendations.

For a proposed basket, PreTrAIde estimates factors relevant to the cost of trading, including bid-ask spread, participation in daily volume and market impact. It also provides portfolio breakdowns and a concentration index. These checks can inform an evaluation of a contemplated change, but they do not replace a period-by-period turnover calculation from actual trading records.

## Common mistakes

- **Adding purchases and sales together:** That counts both sides of many replacement trades under the formula above.
- **Using ending value without checking the denominator:** A changing portfolio value can make ending value misleading compared with an average.
- **Ignoring the measurement period:** A 20% monthly rate and a 20% annual rate describe different activity.
- **Treating turnover as a cost or return:** It measures trading activity; costs and outcomes require separate calculations.
- **Assuming every method matches:** Published turnover figures may use different exclusions, cash treatments or adjustments.

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Source: https://pretraide.com/glossary/portfolio-turnover