P50
P50。満期前のいずれかの時点で取引の最大利益の50%に到達する確率で、とくにプレミアム売り手にとって一般的な利益確定の目安となる。
P50 is the probability of reaching 50% of a trade's maximum profit at some point before expiration, not just at the final bell. It is a path-based, take-profit metric: rather than asking whether the position wins, it asks how likely the market gives you a chance to bank half the best-case gain and walk away early. Because it counts any moment the target is hit, P50 is usually much higher than the plain probability of profit for the same trade.
In practice it is a staple for premium sellers who close winners at half profit rather than holding to expiration. A credit spread might show a 90% P50 even when its probability of max profit is far lower, which is the statistical backbone of the popular "manage at 50%" rule: taking the money early frees capital, cuts the time your risk sits open, and sidesteps the late-cycle gamma that can turn a comfortable winner into a loss. Higher P50 means the profit target is realistically within reach along the way.
The common mistake is reading P50 as a promise of profit rather than of opportunity. Hitting 50% is a chance to exit, not an automatic fill — you still have to place the closing order — and a high P50 says nothing about how large the remaining losses are in the cases that fail. Pair it with max loss and reward-to-risk so a string of managed half-winners is not undone by the trades that never touch the target.
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