Avoiding Lookahead Bias When Timing Backtest Signals and Trades

Summary

This forum post raises a practical backtesting question: whether strategy data indexed by the current date can be used to trade at that same day’s open without introducing lookahead bias. The example ranks stocks using market capitalization, tradable market capitalization, and closing price, while the author notes that some other platforms use the previous trading date for data retrieval. The concern is that a backtest may make an opening trade using information that was not yet available at that time.

The author wonders whether strategies that generate signals after the market close and execute on the following day account for the timing gap in live trading, and whether the backtest engine handles the same timing correctly. The post does not provide an answer or establish BigQuant’s execution semantics. Its value is identifying the need to align each feature’s availability, signal calculation time, and simulated fill time. Without platform-specific scheduling and data-access rules, the example cannot determine whether the described code leaks future information.

Key ideas

• Using a closing-price feature to trade at the same day’s open may create lookahead bias.
• Backtests must align data availability, signal generation, and order execution times.
• A signal generated after the close may be intended for execution on the next trading day.
• The post asks about platform behavior but does not provide a definitive answer.

Tags

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.