A stop loss is the exit you decide in advance, exactly at the price where you think your idea stops being right. It's what turns an open ended loss into a known one, and it sets the 1R that every other number on your trade is measured against. Without one, the market decides how much the trade costs you, and could cost you the whole account.
What is a stop loss?
An order that sits at a price and closes your position when the market gets there. The distance from your entry to that price is your risk on the trade, so it's also your 1R in R multiples. Everything downstream depends on it: your risk reward ratio measures the target against this distance, and position sizing turns it into a quantity.
Where do you put it?
Where the idea is wrong, not where the pain starts. Three methods, and each one gives something up:
| Method | Where the stop goes | What it costs you |
|---|---|---|
| Fixed percentage | the same distance on every trade | it ignores the chart, so it sits too tight in a fast market and too wide in a slow one |
| Structure | beyond the level that proves the idea wrong | the distance changes every trade, so your size has to change with it |
| Volatility | a multiple of the recent range | fewer stop outs on noise, but the risk distance moves as the market does |
Most traders end up combining them: find the level that invalidates the trade, then check if that distance fits your risk per trade budget. If it doesn't, trade smaller or skip it. Modifying the stop to make the trade fit is how you end up with a mess.
Why a tighter stop is not a cheaper one
A tight stop looks like it saves money and usually costs the most. Move it closer and your ratio improves on paper while your win rate falls through the floor, because now ordinary noise closes the trade before the idea gets a chance. You pay the costs on every one of those exits too.
A stop is not a guarantee
It's an instruction, not a promise. Gaps over the weekend, news and thin volume all fill you past the level you asked for, and that gap between the price you wanted and the price you got is slippage. Plan for a loss slightly bigger than 1R, especially if you hold through events.
The habit that breaks accounts
Moving the stop away as price approaches it. One normal movement turns a planned 1R loss into an open ended one, and the trade you already judged becomes a position you're hoping to be back in profit. Setting the level is a decision. Keeping it there is discipline.
Frequently asked questions
Related terms
- R Multiple — Every trade measured against what you risked, where a full stop is always minus 1R.
- Slippage — The gap between the price you expected and the price you actually got.
- Trading Costs — Broker-reported commissions and fees, plus components computed from an exact verified schedule.
- Live vs Backtest — The gap between how a strategy looked in testing and how it performs with real money.