First-Touch Stop/Target Probability Calculator
Under a zero-drift random walk, estimate whether the price is likelier to touch the target or the stop before reaching the end.
Results
Fill in the inputs and click Calculate.
- Target Distance
- –
- Stop Distance
- –
- P(Target First)
- –
- P(Stop First)
- –
Risk disclaimer
Real prices drift, jump and change volatility; this is a simplified path intuition.
Where does this probability come from?
For a driftless random walk, the chance of first touching one side is proportional to the distance to the other side: farther stops raise the probability of hitting the target first.
This is a path-level “first touch” result — not an expiry range probability and not a direction forecast.
How to use
- Enter the current price.
- Enter the stop (below spot) and the target (above spot).
- Click Calculate for both distances and first-touch probabilities.
Formula
- Target distance a = target − spot; stop distance b = spot − stop
- P(target first) = b ÷ (a + b)
- P(stop first) = a ÷ (a + b)
Example
Spot 100, stop 90, target 130 → a=30, b=10 → P(target) 25%, P(stop) 75%.
The farther the target, the likelier the stop hits first; the two always sum to 100%.
FAQ
Why no time dimension?
“First touch” depends only on distances; whether a level is hit within a horizon needs time and volatility — use the range-probability tool.
Is there a directional assumption?
No. It is zero-drift: the price is not assumed to trend up or down.