Through many years of multidiscipline efforts Oklahoma State University researchers have produced Sensor Based for Nitrogen Rate Calculators (SBNRC) for many of the grain crops produced in Oklahoma.  This technology has spread around the world with the bulk of the work focusing on wheat and corn.  In these crops producers have seen the benefits of better nitrogen (N) fertilizer management resulting from either reduced N inputs and cost savings or increased yield from additional inputs.  With the use of a non N limiting reference strip, remote sensors are used to estimate potential grain yield of the reference strip and remaining field midseason.  The mid-season fertilizer rate is then calculated from the difference between the N uptake of the two.  Being able to identify yield potential mid-season allows for the increase of N rates in years were the demand for N is greater and reducing it in years were the environment supplies adequate nitrogen or yield potential is reduced.  In 2006 a study was initiated to develop similar technologies for cotton production.   There are many challenges in taking the technology from grain crops into an indeterminate broadleaf crop.  But with the increase in N cost the development of a method to determine optimum N fertilizer rate would greatly benefit the producers.  This paper walks through the development of the algorithm that will be used in the cotton SBNRC.  The goal of the SBNRC is to deliver a mid-season side dress rate that will maximize yield without causing excess growth.