Quote from panzerman:
To calculate the actual odds at expiration (and under a perfectly Gaussian distribution assumption), put these formulas into Excel.
std. devs. = (ln(future_price/current_price))/(volatility*sqrt(days_til_expiry/252))
probability = normsdist(std. devs.)
The probability is the area under the bell curve to the left of the future_price. The probability of finishing to the right of the future_price is (1-probability).