Calculate the growth of deltas in SQL Server
There are plenty of posts on the Internet with various solutions for this.  A quick search of 'Sql Server Track Database Growth' found this one at the very top.  I haven't vetted it, so due diligence applies.  To summarize:

First create a table to keep the size information of each database with a date on which the information is collected:

CREATE TABLE DatabaseFileSize
(
[database_id] INT,
[file_id] INT,
[file_type_desc] NVARCHAR(120),
[name] NVARCHAR(128),
[physical_name] NVARCHAR(520),
[state_desc] NVARCHAR(120),
[size] INT,
[max_size] INT,
[growth] INT,
[is_sparse] BIT,
[is_percent_growth] BIT,
[collect_date] DATETIME
)
GO


Create a stored procedure to populate this table with the current database size information:

CREATE PROC usp_util_CollectDatabaseSize
AS
BEGIN
SET NOCOUNT ON
INSERT INTO DatabaseFileSize
(
[database_id],
[file_id],
[file_type_desc],
[name],
[physical_name],
[state_desc],
[size],
[max_size],
[growth],
[is_sparse],
[is_percent_growth],
[collect_date]
)
SELECT
[database_id],
[file_id],
[type_desc],
[name],
[physical_name],
[state_desc],
[size],
[max_size],
[growth],
[is_sparse],
[is_percent_growth],
GETDATE()
FROM sys.master_files
SET NOCOUNT OFF
END
GO


Now we need to populate the table over a period of time, so we need to create a SQL Agent job to execute this stored procedure and schedule this job to run everyday.

USE [msdb]
GO
/****** Object:  Job [Collect_Database_Size_Info]    Script Date: 02/13/2013 23:47:43 ******/
BEGIN TRANSACTION
DECLARE @ReturnCode INT
SELECT @ReturnCode = 0
/****** Object:  JobCategory [[Uncategorized (Local)]]]    Script Date: 02/13/2013 23:47:43 ******/
IF NOT EXISTS (SELECT name FROM msdb.dbo.syscategories WHERE name=N'[Uncategorized (Local)]' AND category_class=1)
BEGIN
EXEC @ReturnCode = msdb.dbo.sp_add_category @class=N'JOB', @type=N'LOCAL', @name=N'[Uncategorized (Local)]'
IF (@@ERROR &lt;&gt; 0 OR @ReturnCode &lt;&gt; 0) GOTO QuitWithRollback
END
DECLARE @jobId BINARY(16)
EXEC @ReturnCode =  msdb.dbo.sp_add_job @job_name=N'Collect_Database_Size_Info',
@enabled=1,
@notify_level_eventlog=0,
@notify_level_email=0,
@notify_level_netsend=0,
@notify_level_page=0,
@delete_level=0,
@description=N'No description available.',
@category_name=N'[Uncategorized (Local)]',
@owner_login_name=N'Domain\User', @job_id = @jobId OUTPUT
IF (@@ERROR &lt;&gt; 0 OR @ReturnCode &lt;&gt; 0) GOTO QuitWithRollback
/****** Object:  Step [DBSize]    Script Date: 02/13/2013 23:47:44 ******/
EXEC @ReturnCode = msdb.dbo.sp_add_jobstep @job_id=@jobId, @step_name=N'DBSize',
@step_id=1,
@cmdexec_success_code=0,
@on_success_action=1,
@on_success_step_id=0,
@on_fail_action=2,
@on_fail_step_id=0,
@retry_attempts=0,
@retry_interval=0,
@os_run_priority=0, @subsystem=N'TSQL',
@command=N'EXEC usp_util_CollectDatabaseSize',
@database_name=N'AuditDB',
@flags=0
IF (@@ERROR &lt;&gt; 0 OR @ReturnCode &lt;&gt; 0) GOTO QuitWithRollback
EXEC @ReturnCode = msdb.dbo.sp_update_job @job_id = @jobId, @start_step_id = 1
IF (@@ERROR &lt;&gt; 0 OR @ReturnCode &lt;&gt; 0) GOTO QuitWithRollback
EXEC @ReturnCode = msdb.dbo.sp_add_jobschedule @job_id=@jobId, @name=N'DailyDBSize',
@enabled=1,
@freq_type=4,
@freq_interval=1,
@freq_subday_type=1,
@freq_subday_interval=0,
@freq_relative_interval=0,
@freq_recurrence_factor=0,
@active_start_date=20130213,
@active_end_date=99991231,
@active_start_time=0,
@active_end_time=235959,
@schedule_uid=N'445fb175-517b-4221-b6b8-6c6877dc7c24'
IF (@@ERROR &lt;&gt; 0 OR @ReturnCode &lt;&gt; 0) GOTO QuitWithRollback
EXEC @ReturnCode = msdb.dbo.sp_add_jobserver @job_id = @jobId, @server_name = N'(local)'
IF (@@ERROR &lt;&gt; 0 OR @ReturnCode &lt;&gt; 0) GOTO QuitWithRollback
COMMIT TRANSACTION
GOTO EndSave
QuitWithRollback:
IF (@@TRANCOUNT &gt; 0) ROLLBACK TRANSACTION
EndSave:

GO


Now we have the information over the period of time and we can run our below query to make a report out of this data.

--DB Size Growth Trend
SELECT
DB_NAME(database_id) AS DatabaseName,
collect_date AS CollectionDate,
((SUM(size))*8)/1024 AS DBSizeInMB
FROM DatabaseFileSize
GROUP BY database_id,collect_date
ORDER BY DatabaseName,collect_date

--DB File Size Growth Trend
SELECT DB_NAME(database_id) AS DatabaseName,
(CASE file_type_desc
WHEN 'ROWS' THEN 'Data'
WHEN 'LOG' THEN 'Log'
END) AS FileType,
physical_name AS PhysicalPath,
collect_date AS CollectionDate,
((SUM(size))*8)/1024 AS FileSizeInMB
FROM DatabaseFileSize
GROUP BY database_id,physical_name,file_type_desc,collect_date
ORDER BY DatabaseName,collect_date


If you want to look back in time for database growth, you can use the information in Erin Stellato's blog post Trending Database Growth From Backups

This technique relies on information in msdb.dbo.backupset which is pruned by various maintenance plans and possibly other processes, so you may only be able to go back a few months. Here's the main query from that post:

SELECT
[database_name] AS "Database",
DATEPART(month,[backup_start_date]) AS "Month",
AVG([backup_size]/1024/1024) AS "Backup Size MB",
AVG([compressed_backup_size]/1024/1024) AS "Compressed Backup Size MB",
AVG([backup_size]/[compressed_backup_size]) AS "Compression Ratio"
FROM msdb.dbo.backupset
WHERE [database_name] = N'AdventureWorks'
AND [type] = 'D'
GROUP BY [database_name],DATEPART(mm,[backup_start_date]);