Markets & trading
Transaction costs are the explicit and implicit costs of entering, changing or exiting a position. They include fees, taxes, spread, market impact and sometimes financing or currency conversion.
Make it click
A trip has a headline fare plus booking charges, travel to the station and time lost in queues. Ignoring the less visible parts understates the true cost.
Now put that into markets
A strategy's gross return becomes net return only after realistic implementation. Costs vary with size, liquidity, turnover, venue and market conditions.
Explicit commissions are easy to observe; spread and impact require timestamped quotes and fills. Taxes and settlement effects depend on instrument and jurisdiction.
Model costs using the trade rule and likely capacity, then compare with realised fills. Avoid one flat assumption across unlike assets and periods.
Backtests often understate costs and assume impossible liquidity. A small gross edge can disappear when turnover and impact are included.
Takeaway
