Temporary Price Impact

Temporary price impact arises from the friction of consuming market liquidity. When a large order is executed, it must absorb available liquidity at multiple price levels, pushing the price above (for a buy) or below (for a sell) the level that existed before the trade began. This displacement is not necessarily informational — it reflects the momentary imbalance between the demand for immediate execution and the available supply of willing counterparties at the prevailing price.

After the order is completed, the market often partially or fully reverts toward the pre-trade price. New liquidity providers who were not present during the execution phase re-enter the market, restoring the balance between buyers and sellers. The price level stabilizes at a point that may be somewhat above the pre-trade price (reflecting any permanent information content) but below the intra-order peak price (reflecting the reversal of temporary displacement). The difference between the peak trade price and the post-trade equilibrium price is an empirical measure of the temporary component of total impact.

For execution traders, temporary price impact is the primary driver of the urgency-cost trade-off in algorithmic execution. If an institution must execute a large order rapidly, it will consume liquidity faster than the market can replenish it, paying more in temporary impact. If it executes the same order slowly, it gives the market time to replenish between trades, reducing temporary impact — but it runs the risk that the price moves adversely in the interim due to market conditions changing. This tension between impact cost and timing risk is the fundamental problem that algorithmic execution strategies attempt to optimize.

The Almgren-Chriss optimal execution framework, one of the most influential models in quantitative execution research, explicitly models the trade-off between temporary impact (which grows with execution speed) and timing risk (which grows with execution duration) to identify the optimal execution schedule that minimizes total expected cost. The model parameterizes both the temporary impact function and the volatility of the security to derive a closed-form optimal trajectory — a schedule of how much to trade at each time step that minimizes the expected total cost including both impact and risk.

Empirical estimates of temporary price impact vary considerably across securities and market conditions. In highly liquid large-cap U.S. equities, temporary impact on institutional-sized orders is typically a few basis points per percent of average daily volume traded. In small-cap securities with limited market depth, temporary impact can be an order of magnitude larger for the same relative order size, reflecting the shallower liquidity available to absorb the order without price displacement. These differences in temporary impact across the universe of U.S. equities are a key reason why institutional trading desks allocate significantly more attention to execution strategy in smaller-cap positions.