SQL Server Backup File Size I am regularly backing up the database using the SQL Server UI (Tasks --> Backup) with Backup Type:Full. Each time I backup, the .bak file gets bloated. If I delete the .bak file and do the backup, then 50 MB .bak file is created instead of the 500 MB file that I deleted. 

What is the reason behind this?
You are appending the backup into same file so it is actually accumulating the backups. You need to give a new name each time you trigger backup from Tasks->Backup.

Use maintenance plan as it has timestamp for each backup file or else go with Ola Hellengren's solution.

https://ola.hallengren.com/