Using FX benchmarks to measure execution quality
Overview
Benchmarks are the reference points used in foreign exchange transaction cost analysis (TCA) to evaluate whether a trade was executed efficiently. Since FX markets are decentralized and opaque, benchmarks provide the “yardstick” against which execution outcomes can be measured. The choice of benchmark matters: different benchmarks answer different questions about cost, timing, and effectiveness.
Benchmarks can be single point-in-time reference market prices, average prices over a specific time period, or a combination of benchmarks. Along with the market price at the time of execution, common benchmarks you are already familiar with are the market Open/Hi/Low/Close. While the list of benchmarks is practically limitless, they all fall under four basic concepts: performance measurement, cost assessment, strategy evaluation and regulatory compliance.
Common FX benchmarks
Mid-Market Rate (Spot Mid)
Definition: The midpoint between the best bid and offer at the time of trade.
Use: Provides the cleanest measure of the spread paid, isolating the direct transaction cost.
Limitation: Mid prices can move quickly, so comparisons are sensitive to timing. The source of the best bid and offer is a matter of great importance. If your TCA system is not replicating the interbank market, the mid-market rate is subject to doubt.
Arrival price (decision price): measures drift
Definition: The market rate at the time the bank acknowledges a trade or provides a response to a trade request. In algo trading, it is either the first slice of the algorithm, or, if an algorithm execution is delayed, the first price that is shown by the algo provider.
Use: Evaluates the implementation shortfall — the difference between the decision to trade and the final execution.
Limitation: Requires accurate timestamping of when the decision was made, which is not always straightforward for corporates.
Fixing Rates (e.g., WM/Refinitiv 4 p.m. London fix)
Definition: Widely published benchmark rates calculated over a short trading window (typically one minute). The WM/Refinitiv benchmarks use a five-minute window of +/- 2.5 minutes around the benchmark time.
Use: Commonly used for passive benchmark execution, custody flows, and portfolio valuation. These benchmarks provide a mark to market rate in a 24-hour, OTC market.
Limitation: Susceptible to short-term volatility, particularly around the fixing window. Also subject to “directionality,” especially at month end. Trillions of assets are benchmarked against the WM/Refinitiv 4pm Close, especially index funds. It is only natural for these indices, especially passive indices, to trade in the same direction for month end rebalancing.
Market highs and lows (interval analysis)
Definition: The best and worst prices available during a defined execution window. The most common use is daily range benchmarks.
Use: Provides context for whether the trade outcome was closer to the best or worst market levels. With respect to the daily range, any trade at or outside the worst price of the day would be considered an outlier requiring investigation.
Limitation: Outside of the worst price of the day, range benchmarks are more descriptive than actionable; not a standard for best execution. However, if you do not have accurate timestamps, or no timestamp at all, daily range benchmarks can provide insight into your trading costs using skew analysis.
Trade-Weighted Average Price (TWAP)
Definition: The average price achieved in the market during a specified window, weighted by trade count. A FX substitute for volume-weighted average price (VWAP).
Use: Often used to measure the effectiveness of algorithmic execution strategies but can also be used to measure the trader’s performance if they “work” a trade over a period of time.
Limitation: Requires access to market volume data, which may be less transparent in FX than in equities. In FX markets, VWAP is not possible since it is an OTC market. FX TCA providers count the number of trades or quotes at each price level and create a trade-weighted or quote-weighted average price.
Choosing the right benchmark
For corporates, the appropriate benchmark depends on the objective:
- Cost transparency: Mid-market rates are most relevant.
- Execution efficiency: Arrival price is best for measuring the impact of timing and slippage. AtlasFX refers to this measure as market drift.
- Passive strategies: Fixing benchmarks are useful when aligning with index or accounting standards — a daily mark-to-market.
- Algo performance: VWAP or interval-based benchmarks help evaluate whether execution added or reduced cost.
Conclusion
A robust FX TCA framework uses multiple benchmarks to triangulate execution quality, balancing transparency with practicality. For corporates, this means moving beyond a single reference rate and adopting a layered view of execution outcomes.
