Data Base full backup size - sql

Question

I have a job to full backup my database daily. I have usually between 200 to 300 new records in the database daily. However, size of backup file is always the same and is 7,472 KB. Why this is always fixed while the number of records is increasing. Database Files specifications are as following:
Logical Name ------ File Type----Filegroup---Initial Size----Autogrowth/ Maxsize
DBF-----------------Rows Data----PRIMARY-----4---------------by 15 MB, Unlimited
DBF_Data------------Rows Data----FG_Data-----221-------------by 15 MB, Unlimited
DBF_Index-----------Rows Data----FG_Index----3---------------by 15 MB, Unlimited
DBF_Log-------------Log--------Not Applicable- 793--------- by 10 percent,Limited to 2097152 MB
This is the code I wrote to make daily backup
declare #Date nvarchar(10)
select #Date=cast( cast(getdate() as date) as nvarchar)
declare #Path nvarchar(100)
select #Path= 'C:\PAT Daily BK\PAT' + #Date +'.Bak'
BACKUP DATABASE PAT TO DISK =#path

Answer 1

Until your database expands past the initial size, all backups will be the initial size (compression aside). After it starts expanding, if the expansion amount is set to an amount greater than the space consumed by the additional records then the backup can be expected to stay the same size for multiple days, but eventually will increase when it has to expand again.
SQL Server databases occupy all space allocated whether the data warrants it or not. After it uses up that space it will follow the rules you set for expansion.
Update: The above explains the observed behavior for encrypted databases, but not for unencrypted databases, as backups of unencrypted databases will be relative to the size of the database.