Methods for estimating an unknown value for a dynamic under-balance condition are herein disclosed. The unknown value may be a well property value, or may be a transient pressure characteristic. Embodiments of the method include selecting at least one transient pressure characteristic and selecting at least one well property value. A correlation between the at least one transient pressure characteristic and at least one well property value is obtained. The unknown value is estimated by applying at least one known transient pressure characteristic or at least one known well property value to the obtained correlation.