Formula to find cumulative probability from z-score

I want a formula to calculate the cumulative normal probability from a given z-score. e.g. f(1) = 0.3413, but I can live with f(0.3413) = 1

I don't want to use a table.

I don't know or want to learn integral calculus for this, but I can use a Basic iterative program loop if required.

I used to have a calculator (radio shack EC-4004 circa 1988) that provided a formula to approximate the value as a sample program, but the manual is lost and I can't even remember the name of the mathematician credited for the formula.

Thanks for any help.