4.7 GB used, cannot back up

Has anyone had the issue where they have only used 4.7 GB out of 5, but your IPhone won’t back up because “there isn’t enough Icloud storage”?? I could see if it was 4.9 or more, but I am clearly under the 5.0. I have restarted the phone. Then I get the reminder that I haven’t backed up every five minutes! Thank you