Windows Backup Retention: Server 2012 R2 Essentials

Hi,

We are backing up a Server 2012 R2 Essentials machine's files and folders, using Windows Server Backup, to an external hard drive. That backup drive is now 84% full. It is my understanding that Windows Server Backup will automatically delete old backups when necessary, but does anybody know at what point that happens? When the target reaches 90%?

Thanks.