Space used on time machine drive not changing over time

My specified time machine location is on an external hard drive. Despite it backing up frequently, in which it shows regularly backing up sizes of over 1GB, the amount used on the disk has not changed for months. This does not make sense, the time machine menu even notes that oldest backups will be deleted once the disk is full (the disk is nowhere near full). The amount of space used on this time machine allocated disk should get smaller as more backups are added.