P = a probability value (0 < P < 1)
The inverse of the cumulative standard normal distribution function. NORMSINV returns the value X such that the integral from minus infinity to X of the standard normal distribution function is equal to P. P must be greater than 0 and less than 1.
The mathematical formulation is given by:
NORMSINV(0.5) = 0
NORMSINV(0.975) = 1.959964
NORMSINV(NORMSDIST(0.88)) = 0.88
NORMSINV(1) = Error
Excel function: NORMSINV