What is a stop-loss (and why it matters)
Updated May 15, 2026
The definition
A stop-loss is a price level at which you exit a losing trade, decided before you enter. It can be a resting order with your broker that triggers automatically, or a mental line you commit to honoring. Either way, its job is the same: to take the decision out of your hands at the worst possible moment, when a position is moving against you and the temptation to "give it room" is strongest.
Why it matters more than your entry
New traders obsess over entries, but the stop is what keeps you in the game. A single oversized loss can wipe out the gains from many good trades. The math is unforgiving: a 50% loss requires a 100% gain just to break even. Capping losses early means no single mistake can take you out, which matters far more over a career than nailing any one entry.
Where to place it
A stop belongs at the price that proves your idea wrong — just beyond the support you bought at, or above the resistance you shorted. Place it where being hit means the setup has genuinely failed, not at an arbitrary round number. If a stop sits so close that normal price noise triggers it, your position size is probably too large for that level.
Stops and position sizing
The distance from your entry to your stop is your risk per share. Combined with how much of your account you're willing to lose on the trade, that distance tells you exactly how big the position should be — the core of risk management. Every AlphaForecast forecast includes a stop level so you always have a defined point of invalidation to build a plan around.