Stop-losses: the one order that forces you to act when your emotions won’t let you

Most people can explain what a stop-loss is. Very few use one consistently. The gap between knowing and doing is where most trading losses happen, and understanding why that gap exists is the real lesson here.

Reviewed by James Whitfield, Senior Editor · May 14, 2026, 05:46

The mechanics are straightforward. The psychology is where it gets complicated.

How a stop-loss order works

A stop-loss order is an instruction you give your broker to sell a share automatically if the price falls to a set level. Buy a share at 200p. Set a stop at 180p. If the price drops to 180p, your broker sells without you having to act. You have capped your loss at 10 per cent.

The reason most investors do not use stop-losses comes down to hope. When a share you own starts to fall, the natural response is to tell yourself it will recover. Sometimes it does. But sometimes it falls to 150p, then 120p. By the time you accept something has gone wrong, you are sitting on a loss you could have avoided.

Behavioural finance has a name for this pattern: the disposition effect. People sell winning positions too early, locking in gains before they grow. They hold losing positions too long, waiting for a recovery that may never come. The FCA has observed that this asymmetry is one of the most consistent patterns in retail investor behaviour. A stop-loss is the mechanical answer to the second half of that problem.

Getting the level right

The 10 per cent rule is a common starting point. Set your stop-loss order at 10 per cent below your purchase price. If the share falls through that level, you are out. It is not a magic number. Some investors use 8 per cent, some 15, depending on how volatile their holdings tend to be.

A FTSE 100 blue chip might justify a tighter stop than an AIM-listed small-cap that moves several percentage points on an ordinary trading day. The point of a specific figure is not precision; it is commitment.

Setting the stop too tight creates its own problem. A share that oscillates 5 per cent on normal trading days will trigger a stop set at that level through routine market noise alone. Nothing has changed fundamentally. You have been knocked out of a perfectly good position and will watch the price recover without you.

Set the stop too loose and it provides little real protection. A 30 per cent stop on a speculative small-cap might represent a position that should have been cut at 15 per cent. The level needs to limit damage meaningfully, but leave enough room for a position to breathe through ordinary market movements.

For investors running a portfolio across multiple holdings, consistent stop-loss discipline matters particularly. A single position running without a stop can, in a bad run of news, erase the gains from several positions that went well. The discipline applies regardless of whether you hold shares in an ISA or a general investment account.

When to set your stop-loss order

Where you place the stop matters less than when you place it. The rule most experienced investors follow is to set the stop at the point of purchase, not after the price starts falling.

Once a share is moving down, emotion enters the calculation. You will find reasons to hold on just a little longer. Setting a stop-loss order on the day you buy is a very different exercise from trying to set one after a 7 per cent fall. When you are thinking clearly, you set a level. When you are looking at a loss on screen, you rationalise.

This is what makes a stop-loss order genuinely useful, even as a purely psychological tool. It forces you to answer a question before emotion distorts your thinking: at what price is your original investment case broken? Say you bought a retailer at 400p because you believed management would turn around profit margins. The share falls to 360p. Does that thesis still hold?

Stop-loss orders versus stop-limit orders

There is a practical distinction worth understanding. A straightforward stop-loss order converts to a market order when the trigger price is reached. You sell at whatever the market price happens to be at that moment.

In a fast-moving market, or on a thinly traded share, that can be significantly below your trigger price. Traders call this slippage. A stop-limit order adds a floor below the trigger: you will not sell below a certain level. The catch is that if the price falls through both levels quickly, your order may not execute at all.

For most retail investors, the trade-off is reliability versus control. A stop-loss is more likely to execute. A stop-limit gives more price control but may fail to execute in a fast-moving market.

When a stop-loss order triggers: sell

One thing catches people out. When a stop-loss order triggers, sell. The whole point of a pre-commitment device is that you honour it. The moment you override a triggered stop because you still believe in the share, you have turned a mechanical discipline back into an emotional decision.

A stop-loss that is negotiable is not a stop-loss.

None of this means a stop-loss guarantees you will not lose money. It means you decide in advance how much you are willing to lose on any single position. You commit to that before the market tests your resolve. Over a full portfolio, that discipline compounds. The investor who cuts losses consistently at a set level will, on average, survive the bad calls long enough for the good ones to matter.

The Short Version

• A stop-loss is a standing instruction to sell a share automatically if it falls to a set price, removing the emotional decision at the worst possible moment.
• The 10 per cent rule is a common starting point, though the right level depends on how volatile the share tends to be in normal trading.
• Set stops too tight and routine market fluctuations knock you out of good positions; set them too loose and the stop-loss provides little real protection.
• Always set your stop-loss at the point of purchase, not after the price has already started falling, when emotion will distort the decision.
• A stop-limit order adds a minimum sell price below the trigger, which can improve outcomes on liquid shares but risks non-execution in fast markets.
• When a stop-loss triggers, sell. A stop-loss you override is not a stop-loss.

Related reads

• how the bid-offer spread affects trading costs
• how to decide when to take profits
• how a balanced portfolio helps manage risk

Nothing in this article is financial advice. Tax rules change frequently. Check the current ISA allowance, CGT exemption and relevant rules on HMRC’s website or consult a qualified financial adviser for your specific situation.

Money & Markets is a guide to personal finance and investing for people who want to understand the world they live in, updated as rules and markets change.

Disclaimer: The value of investments can go down as well as up, and you may get back less than you invest. This article is for informational and educational purposes only and does not constitute financial advice. Always do your own research and consider seeking independent advice before making any investment decision.