Implementation Shortfall

In trading terms, an implementation shortfall is the difference between the prevailing price or value when a buy or sell decision is made with regard to a security and the final execution price or value after taking into consideration all commissions, fees and taxes. As such, implementation shortfall is the sum of execution costs and the opportunity cost incurred in case of adverse market movement between the time of the trading decision and order execution.

In order to maximize the potential for profit, investors aim to keep implementation shortfall as low as possible. Investors have been helped in this endeavor over the past two decades by developments such as discount brokerages, online trading and access to real-time quotes and information. Implementation shortfall is an inevitable aspect of trading, whether it be stocks, forex, or futures. Slippage is when you get a different price than expected on an entry or exit from a trade.

If the bid-ask spread in a stock is $49.36/$49.37, and a trader places a market order to buy 500 shares, the trader may expect it to fill at $49.37. However, in the fraction of a second it takes for your order to reach the exchange, something may change or perhaps the traders's quote is slightly delayed. The price the trader actually gets may be $49.40. The $0.03 difference between their expected price of $49.37 and the $49.40 price they actually end up buying at is the implementation shortfall.

Implementation shortfalls often occur when a trader uses market orders to buy or sell a position. To help eliminate or reduce it, traders use limit orders instead of market orders. A limit order only fills at the price you want, or better. Unlike a market order, it won't fill at a worse price. Using a limit order is an easy way to avoid implementation shortfall, but it's not always the best option.

When entering a position, traders will often use limit orders and stop limit orders. With these order types, if you can't get the price you want, then you simply don't trade. Sometimes using a limit order will result in missing a lucrative opportunity, but such risks are often offset by avoiding implementation shortfall. A market order assures you get into the trade, but there is a possibility you will do so at a higher price than expected. Traders should plan their trades, so they can use limit or stop limit orders to enter positions.

When exiting a position, a trader typically has less control than when entering a trade. Thus, it may be necessary to use a market orders to get out of a position quickly if the market is in a volatile mood. Limit orders should be used in more favorable conditions.