A method for determining the remaining time a fluid in a container can be used. The method includes: determining the amount of fluid in the container; and determining the remaining time based on the amount of fluid in the container. Preferably, the step of determining the remaining time is calculated by using the determined amount of fluid and a predetermined first correlation of remaining time vs. amount of fluid in the container. In a preferred embodiment, the fluid is a reagent in a reagent pack used in a diagnostic analyzer. A method for measuring the presence or concentration of an analyte in a sample on an automated diagnostic analyzer includes: providing a reagent storage container on the analyzer; providing a measurement station for taking a measurement of the sample; determining the amount of reagent remaining in a reagent storage container; calculating the remaining time of the reagent by using the determined amount of reagent and a predetermined first correlation of remaining time vs. amount of fluid in the container; if the time the reagent has been in the reagent container is greater than the remaining time, then discarding the reagent, otherwise adding reagent to the sample; and taking a measurement of the sample to determine the presence or concentration of the analyte.