what is a guaranteed stop loss, when should i use it?

A guaranteed stop loss offers you protection against price gapping, which is a scenario where price jumps over your specified stop price without any trading taking place.

Ordinary stop losses are exposed to the risk of gapping, but guaranteed stops aren't, & that is why your broker will charge you a fee after executing your guaranteed stop.

Price gapping is not the fault of your broker; it is a common market phenomenon caused by the release of breaking news such as NFP, CPI, Interest Rate Decisions, Political Events, etc.

Imagine you set a stop loss at 1.0004 and price suddenly gaps to 1.0001, your broker will have to execute your stop loss at 1.0001 causing you to lose an extra 3 pips more than what you bargained for. Guaranteed stops work to protect you from this kind of price gapping.

I use guaranteed stops when i am trading high volumes/big lot sizes because even a 1 pip price gap can mean a significant loss when trading large volumes.

I never trade NFP, CPI without using a guaranteed stop, I mean the broker only charges me for it if the slippage does happen so why wont I use it? Its one tool that lots of traders ignore. I once traded cpi and my stop loss was not executed until i had lost over 35 pips and ever since that experience, I never traded news events without a guaranteed stop.

I use guaranteed stops when i am worried that price slippage may occur. My current broker (Trade Nation) allows me set guaranteed stops and its not even that expensive.