The correct answer is D . Portfolio turnover measures the extent to which securities within a portfolio are bought and sold. A high turnover rate generally means more transactions, and more transactions can generate additional commissions, bid-ask spread costs, market-impact costs and other trading expenses. Because those costs are deducted from portfolio assets or otherwise borne by investors, they create a drag on net investment returns .

The CIRE syllabus explicitly requires candidates to understand the “potential impact of fees, turnover and taxes on the client's investment returns.” This principle is especially important when comparing active and passive investment approaches: an active portfolio may generate value through successful security selection, but the gross excess return must be sufficient to overcome any additional costs created by increased trading.

A is incorrect because higher turnover can actually accelerate taxable realizations in non-registered accounts rather than automatically reducing tax. B is incorrect because trading more frequently provides no guarantee of superior performance. C is also incorrect because turnover by itself does not systematically reduce portfolio risk; the effect on risk depends on what securities are purchased and sold and the resulting portfolio exposures.

CIRO enforcement materials have also emphasized that excessive transaction costs can materially reduce the investment benefits received by clients.

Study Guide Reference: CIRE Element 2.9 — impact of fees, portfolio turnover and taxes on client investment returns.