Query to calculate database growth

I have the following query that outputs some good information from MDW data collectors regarding database space usage. I am wondering with the following columns (db size, reserved space, unused space, unallocated space, collection date) how can i properly calculate database growth trend? I am trying to keep whether a db shrinks or grows into consideration so I cannot just take "max size" and go from that. Here is the full query so far... DECLARE @ServerName VARCHAR(MAX); DECLARE @SelectedDatabaseName VARCHAR(MAX); DECLARE @snapshot_id INT; SELECT TOP 1 @snapshot_id = snapshot_id FROM ( SELECT DISTINCT TOP 100 d.snapshot_id FROM snapshots.disk_usage d , core.snapshots ss --WHERE ss.instance_name = @ServerName --AND ss.snapshot_id = d.snapshot_id ORDER BY d.snapshot_id DESC ) AS q ORDER BY snapshot_id ASC; SELECT database_name , ss.instance_name , CONVERT (DATETIME, SWITCHOFFSET(CAST (d.collection_time AS DATETIMEOFFSET), '+00:00')) AS collection_time , d.snapshot_id , ( ( CONVERT(DEC(15, 2), d.dbsize) + CONVERT(DEC(15, 2), d.logsize) ) * 8192 / 1048576.0 ) AS 'database_size_mb' , 'reserved_mb' = ( d.reservedpages * 8192 / 1048576.0 ) , 'data_mb' = CONVERT(DEC(15, 2), d.pages) * 8192 / 1048576.0 , 'index_mb' = ( d.usedpages - d.pages ) * 8192 / 1048576.0 , 'unused_mb' = ( ( CONVERT(DEC(15, 2), d.reservedpages) - CONVERT(DEC(15, 2), d.usedpages) ) * 8192 / 1048576.0 ) , 'unallocated_space_mb' = ( CASE WHEN d.dbsize >= d.reservedpages THEN ( CONVERT (DEC(15, 2), d.dbsize) - CONVERT (DEC(15, 2), d.reservedpages) ) * 8192 / 1048576.0 ELSE 0 END ) FROM snapshots.disk_usage d , core.snapshots ss WHERE --database_name =@SelectedDatabaseName /*AND*/ d.snapshot_id >= @snapshot_id --AND ss.instance_name = @ServerName AND d.snapshot_id = ss.snapshot_id ORDER BY d.database_name ASC , collection_time; Hopefully at the end of it I will be able to see in a year from now how much every instance, database and server grows per year.