Portfolio Turnover Cost Calculator
Transaction costs drag from portfolio turnover.
Calculate annual cost drag from portfolio turnover based on commission per trade and bid-ask spread — the friction you can't see on a statement.
What this tool does
This calculator models the annual cost drag created by trading friction in an actively managed portfolio. It combines two sources of friction—commissions charged per trade and the bid-ask spread—to show the total cost impact on portfolio returns each year. The result estimates how much of your portfolio value is consumed by transaction costs given your annual turnover rate. Portfolio value, turnover percentage, and spread size are the primary drivers of the total cost. For example, a portfolio turning over 50% annually with 0.1% commissions and 0.05% bid-ask spreads will experience a different cost drag than one turning over 100% annually. The calculation assumes each trade incurs both costs simultaneously and does not account for tax effects, market impact beyond the spread, or timing variation in execution. This is for educational illustration of how trading frequency and friction interact.
Quick answer: with the default values, the result is $250.00 (Annual Cost Drag). Adjust the values below for your own figures.
Enter Values
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Formula Used
Disclaimer
Results are estimates for educational purposes only. They do not constitute financial advice. Consult a qualified professional before making financial decisions.
A 100,000 portfolio turning over 50% a year, with 0.2% commission and 0.1% spread, carries roughly 250 in annual trading friction. At 100% turnover that figure doubles to about 500. Morningstar research has linked higher turnover to greater cost drag before fees, which can matter on a real-return basis over time.
Quick example
With portfolio value of 100,000 and annual turnover of 50% (plus commission per trade of 0.2% and bid-ask spread of 0.1%), the result is 250.00. Change any figure and watch the output shift — it's often more useful to see the pattern than to memorise the formula.
Which inputs matter most
You enter Portfolio Value, Annual Turnover, Commission per Trade, and Bid-Ask Spread. The cost is a straight product of all four, so each one scales the result: double the turnover and the cost doubles, halve the spread and the spread's share falls. Commission counts twice because a round trip means both a buy and a sell. Test this by changing one input at a time.
What's happening under the hood
Round-trip cost × turnover. The formula is listed in full below. If the number looks off, you can retrace the calculation by hand — that's the point of showing the working.
Where this fits in planning
This is a "what-if" tool, not a forecast. It helps to test ideas: what happens to the result as the Portfolio Value or the Annual Turnover changes. The value is in the scenarios you run, not the single answer you get from the defaults.
What this doesn't capture
This is a simplified model that holds its assumptions constant. Real outcomes vary with market conditions, costs, taxes, and timing, so the figure is best read as one scenario rather than a forecast.
Where to go next
This calculation rarely sits alone in a planning exercise. If you're running these numbers, related tools include the index fund vs active fund cost, the investment fee drag calculator, and the portfolio rebalancing frequency calculator — each one answers a different question in the same territory.
Your portfolio's annual transaction costs from 50% turnover reach $250.00, combining commission and spread impacts.
Inputs
| Drag % | 0.25% |
|---|---|
| Portfolio Value | $100,000.00 |
| Annual Turnover | 50.00% |
| Round-Trip Cost | 0.50% |
This example uses typical values for illustration. Adjust the inputs above to match a specific situation and see how the result changes.
Sources & Methodology
Methodology
This calculator estimates the annual cost impact of portfolio turnover by computing the product of your portfolio value, the annual turnover ratio, and the total per-trade friction. The model applies a round-trip cost structure: commission is counted twice, once for the purchase leg and once for the sale leg, while the bid-ask spread is applied once per round trip. The calculator assumes turnover occurs uniformly throughout the year, that commission and spread rates remain constant, and that all positions turned over incur identical costs. The computation does not model tax effects, timing of trades, market impact costs beyond the spread, portfolio rebalancing patterns, or how costs vary with order size or market conditions. Results represent a simplified estimate of trading friction and should be viewed as directional rather than exhaustive.
References
Frequently Asked Questions
Index fund turnover?
High turnover ETFs?
Tax cost too?
Tracking difference?
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