This paper proposes, for query optimizing on Data warehouses, the use of range-encoded bitmap index to calculate aggregates. By using space optimal range-encoded bitmap index for range and aggregate predicates, the need of separate indexes for these operations can be eliminated. The proposed algorithm also uses the population ratio of 1’s in a bitmap to decide whether the bitmap has to be scanned from the disk at all; thus exploiting the opportunity of skipping many bitmap scans since processing them does not affect the solution. These optimizations result in significant improvement in query evaluation time.