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.
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Formula Used
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Disclaimer
Results are estimates for educational purposes only. They do not constitute financial advice. Consult a qualified professional before making financial decisions.
100,000 portfolio, 50% annual turnover, 0.2% commission + 0.1% spread round-trip: 150/year cost. 100% turnover doubles to 300. Active managers averaging 100%+ turnover face 0.5-1%+ drag before fees — significant on real-return basis.
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 rate and the time horizon usually dominate — compounding means a small change in either reshapes the final figure more than a similar shift in contribution size. Test this by doubling 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. Use it to test ideas before committing: what happens if the rate is 2% lower than hoped, what happens if you add five more years. The value is in the scenarios you run, not the single answer you get from the defaults.
What this doesn't capture
Steady-rate math ignores real-world volatility. Actual returns are lumpy; sequence-of-returns risk matters most in drawdown; fees and taxes drag on compound growth; and behaviour changes in drawdowns can reduce outcomes below the projection. The number represents 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, you'll probably also want 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. Treating them as a set rather than in isolation usually produces a more honest picture.
Your portfolio's annual transaction costs from 50 turnover reach 250.00, combining commission and spread impacts.
Inputs
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, multiplying the sum of commission and spread by two to account for both the purchase and sale legs of each transaction. 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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