What Is Slippage In Trading? (The Hidden Cost)

Last Updated on December 11, 2021 by Oddmund Groette

What is slippage in trading? Slippage is a hidden cost that is difficult to quantify. It’s the difference between a theoretical price and the price you get in real and live trading.

What is slippage in trading?

Slippage is the difference between fictional results when testing strategies, and the actual results in real life adjusting for commissions and transaction costs. It’s a “hidden” cost.

Commissions are a cost we know. However, costs related to buying and selling are not always easy to measure. When you backtest a strategy, the entry and close are estimated on an executed price.

But in real life, you never get those prices. If your test shows an entry on 100, in live trading this strategy might buy those shares at 100.02 – not 100. That means your strategy will be less profitable than when testing. This is slippage!

For example, Apple might have a bid of 172.02 and an offer at 172.09. If you want to go long, what price will you bid at? Will you hit the offer price and buy at the market or will you bid at 172.05?

If you bid 172.05 you might get a better price, but you also risk not buying at all unless someone hits your bid. This is slippage. It’s a hidden cost that a backtest can’t capture.

My experience tells me that the backtest results are always much better than real trading. As a rule of thumb, I anticipate that my backtests will result in 50% lower profits in live trading. Not only because of slippage but also because of the ever-changing market cycles. Testing strategies always curve fits more than you think.

Slippage in trading is normally worse than most traders realize. When you backtest, always be prepared and assume that slippage goes against you.