CP command with more options

I want to copy all home folder with sub-folders to /mnt/backup folder everyday at midnight. So, I used cp -R /home/* /mnt/backup/ command and make a script and put it in the cron. First night, it works. But second night, it did not work because it prompted for overwrite. I have used –force but still prompt for overwrite. How can I bypass for overwrite? I looked at the man for cp but did not help me.
I am using Redhat 7.3.
Thanks in advance.