Temporal expressions are widely used in our daily life. Calendar algebra has been studied for years to provide a formal specification for constructing temporal expressions. However, temporal requirements specified by human beings tend to be ill-defined or uncertain. To deal with such kind of uncertain information, we propose the fuzzy calendar algebra which allows users to describe desired temporal expressions easily and naturally. The operations provided reflect the way in which people reason about temporal requirements in daily life. By using the fuzzy calendar algebra, users can define complicated calendars with multiple time granularities in which different time intervals can have different weights according to their matching degrees to the specified calendar. This can help users to discover the knowledge in the time intervals that are of interest to them. We show the usefulness of the algebra by incorporating it with an incremental data miner to mine fuzzy temporal association rules from temporal databases.