A system, a method and a computer program to predict a portion of used lubricant in an engine that is to be drained and replaced by fresh lubricant based on an analysis parameter value that is measured in a sample of used engine lubricant from the engine. The system includes a first input that receives the analysis parameter value from the used lubricant and stores the analysis parameter value in a memory of a processor. A second input receives an analysis parameter threshold value for the used lubricant at the end of a service interval and stores the analysis parameter threshold value in a memory of the processor. A determiner predicts a future analysis parameter value of a mixture of used and fresh lubricant at the end of the service interval based on the analysis parameter value, and the analysis parameter threshold value.