© 2016 American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The spin-axis tilt, which is also known as dynamic imbalance or coning error, is one of the most significant bias errors deteriorating the attitude determination accuracy for spinning spacecrafts. Although it is a common practical issue for spin spacecraft missions, estimation algorithms for the dynamic imbalance have not been studied and issued well. This paper proposes a simple algorithm for spin-axis tilt estimation. The algorithm is based on the Singular Value Decomposition (SVD) and makes use of the attitude rates estimated by an Unscented Kalman Filter (UKF), along with the star scanner measurements. Its accuracy is demonstrated using the models for the Exploration of Energization and Radiation in Geospace (ERG) spacecraft. Other bias errors’ effects on the estimation accuracy are examined and the results are compared with a straightforward averaging approach for dynamic imbalance calculation.