Reconcile one-way turnover with gross traded value, estimate costs on the correct trade base, and distinguish a rebalance ledger from reported fund turnover.
Portfolio turnover
Portfolio turnover measures how much a portfolio trades relative to its size over a stated period or rebalance. It connects a strategy's desired positions to its implementation burden: two strategies with similar paper returns may require very different amounts of trading, and therefore face different transaction costs.
A turnover percentage is incomplete without its counting convention, denominator and time interval. A single rebalance's one-way turnover, its gross traded value and a fund's reported annual turnover can be different numbers describing related activity.
The same USD100 moves through two trades
Consider a synthetic long-only portfolio with USD1,000 of pre-trade net asset value (NAV). Holding A is worth USD600 and B is worth USD400. The target is an equal-weighted portfolio: USD500 in each holding.
Assume no external cash flows, unchanged execution prices, fractional holdings and no costs. Positive trade values mean purchases; negative values mean sales.
Holding
Pre-trade value (USD)
Target value (USD)
Signed trade (USD)
A
600
500
−100
B
400
500
+100
Total
1,000
1,000
0
Selling USD100 of A funds the USD100 purchase of B. One-way turnover is 10%: USD100 was reallocated out of a USD1,000 portfolio. Gross traded value is USD200, or 20% of NAV, because that measure counts both trade legs.
A USD1,000 portfolio sells USD100 of A and buys USD100 of B, moving from 60/40 to 50/50. One-way turnover is 10%; gross traded value is 20% of NAV.
Original synthetic USD ledger. The sale and purchase refer to the same USD100 reallocation. Prices are unchanged, with no external flows or costs; the figure counts trade values, not numbers of shares.
Why the formula has a half
Let wi− be holding i's actual portfolio weight immediately before trading, and wi∗ its target weight. For this costless, fully invested, long-only reset at a common positive NAV V, define
Both weight vectors sum to one, so the signed trades sum to zero. Total purchases equal total sales exactly under these assumptions. Halving the absolute trade total therefore counts the amount reallocated once. Here,
Tone-way=21(∣0.50−0.60∣+∣0.50−0.40∣)=0.10=10%.
The gross traded-value ratio, also called two-way turnover under this convention, omits the half:
Tgross=V∑i∣Δi∣=2Tone-way=20%.
Use actual pre-trade weights rather than last period's target. Relative price moves can change weights without any trades; restoring the previous target can then require rebalancing turnover even though the target itself is unchanged. A buy-and-hold strategy can have changing weights and zero trading turnover.
For a single reset between fully invested long-only allocations, one-way turnover lies between zero and 100%. It is zero when the holdings already match the target and 100% when all capital moves to entirely different holdings. Cumulative turnover over multiple rebalances can exceed 100%. The single-reset bound does not automatically extend to leveraged or short portfolios, or to definitions that count cash differently. At zero NAV, weights and this turnover ratio are undefined.
SelfMadeQuant's Turnover and the Information Horizon develops weight drift and then connects trading demand to changes in forecasts. The public page is a preview; the full lesson requires membership.
Turnover is an input to a cost estimate
Suppose, separately from the costless ledger, that a simplified cost model charges 10 basis points on every dollar bought or sold. Applying that stipulated rate to the gross USD200 traded gives
The 10% turnover, 10 bps cost rate per traded dollar and 2 bps cost relative to NAV are three different quantities. Applying the 10 bps rate only to the one-way USD100 would omit one charged trade leg. This is a stipulated linear estimate, not a market fee schedule: spreads, commissions and market impact can vary across trades.
The USD500/USD500 target above remains a before-cost calculation. Paying costs from the portfolio changes its cash budget and post-cost NAV; an executable reset would need to account for that funding rather than silently retaining every costless equality.
Reading a fund's reported number
A published fund turnover rate follows its disclosure rules, which may differ from this event-level weight formula. Check the jurisdiction, prospectus methodology, measurement period, included instruments and averaging basis before comparing funds or matching a report to a backtest.
For example, the US SEC's Form N-1A, Item 13 instructions specifies the lesser of annual purchases or sales divided by the monthly average value of portfolio securities. It prescribes the averaging calculation and excludes securities whose maturity or expiry at acquisition is one year or less, with further transaction-specific rules. The denominator is the specified portfolio-securities value, not an arbitrary end-of-year NAV. This US reporting convention is not a universal definition of turnover.
Finally, the reciprocal of annual turnover is sometimes used as a rough holding-period intuition under steady replacement assumptions. It does not reveal the age of each position: a stable core and a frequently traded sleeve can generate the same aggregate turnover as more evenly distributed replacement. Turnover measures trading activity; interpreting it also requires knowing what traded and why.
US Securities and Exchange Commission, Form N-1A, Item 13, Instructions 4(d)(i)–(iv), printed p. 27: fund turnover calculation and instrument exclusions. SEC reference copy checked 26 October 2026; reporting conventions should be read in the applicable fund's current disclosures.
