asa241, a Python code which computes the inverse of the Normal Cumulative Density Function (CDF), by Michael Wichura;

ASA241 is Applied Statistics Algorithm 241.

The code includes two routines, R4_NORMAL_01_CDF_INVERSE, and R8_NORMAL_01_CDF_INVERSE, suitable for single or double precision arithmetic calculations.


The computer code and data files described and made available on this web page are distributed under the MIT license


asa241 is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version and a Python version.

Related Data and codes:

prob, a Python code which contains routines for evaluating and inverting the normal CDF, and many other distributions.

test_values, a Python code which contains routines that store selected values of the normal CDF, and many other statistical distributions.


Original FORTRAN77 version by Michael Wichura; Python version by John Burkardt.


  1. Michael Wichura,
    Algorithm AS 241: The Percentage Points of the Normal Distribution,
    Applied Statistics,
    Volume 37, Number 3, 1988, pages 477-484.

Source Code:

Last revised on 09 August 2018.