A method of monitoring soot mass in a particulate filter of an exhaust system includes determining a pressure differential across the filter, obtaining a first soot mass estimate by fitting the determined pressure differential to a first stored database of measured or modeled pressure differentials and corresponding measured soot masses taken during filter regeneration using a substantially similar filter previously loaded following a complete filter regeneration, and obtaining a second soot mass estimate by fitting the determined pressure differential to a second stored database of measured or modeled pressure differentials and corresponding measured soot masses taken during filter regeneration using a substantially similar filter loaded following an incomplete filter regeneration. Actual soot mass is estimated by calculating a weighted sum of the first and second soot mass estimates with weighting based on operating parameters indicative of regeneration efficiency. A monitoring system for a particulate filter is also provided.