In the standard formulation of the Kalman filter, target maneuver (acceleration) is assumed to be a random process that can be modeled as zero-mean additive white noise in the filter plant model. In the optimal reduced state estimator (ORSE) recently introduced by Mookerjee and Reifler, target maneuver is assumed to be a deterministic parameter in the plant model, equal to the maximum target acceleration. In this paper we exploit the steady-state equivalency of the Kalman filter and ORSE to derive an exact analytic expression relating the random tracking index of the Kalman filter, Λ R , and the deterministic tracking index of the ORSE, Λ D . The relationship offers a solution to a central problem in target tracking theory, namely how should the white plant noise level for a Kalman filter be selected for minimum mean square error state estimates in the presence of maximum target acceleration? Using the new relationship, a Kalman filter can be constructed with identical steady-state performance to the ORSE but without the additional computational complexity of the ORSE.