What is Decision price?

The decision price is the market price observed when the investment choice is made, before the order enters the market. It represents the theoretical return of the idea if it could be implemented instantly with no cost.

This baseline is central to implementation shortfall, which compares realized execution to this pre-trade point to quantify total cost.

Establishing the baseline

Firms define a precise time and source for decision prices: a consolidated mid, a last trade, or an index-based fair value. The selection should reflect the data available to the decision maker and be recorded in an auditable way.

For portfolio rebalances driven by models, the decision time may be a scheduled cut. For discretionary trades, it is the time the order ticket is approved.

Role in portfolio workflows

Decision prices guide budgeting for slippage and impact. They also allow performance attribution to separate alpha generation from trading costs. Strategy reviews examine gaps between decision and arrival prices to detect delays and operational bottlenecks.

On the broker side, reporting often includes both decision- and arrival-based metrics so clients can see pre-trade drift as well as execution effects.

Biases and maintenance

If decision times are inconsistent or influenced by previewing order books, results may look better or worse than reality. Clock skew, stale quotes, or selective venue sampling can introduce bias.

Teams maintain governance by logging decision metadata, validating data sources, and periodically auditing the gap between decision and arrival to ensure integrity.

Things to Remember

• Pre-trade anchor: The decision price precedes any market action and frames implementation shortfall.
• Document the source: Record the venue mix and quote type to keep the baseline reproducible.
• Watch for drift: Large gaps to arrival hint at delays or market moves before execution starts.
• Audit regularly: Data integrity checks keep results fair across strategies and teams.