Backups are automatically-created disk images of Droplets. Enabling backups for Droplets enables system-level backups at weekly or daily intervals, which provides a way to revert to an older state or create new Droplets.
Enabling weekly backups for a Droplet adds 20% of the Droplet's cost per month.
Daily backups are available to Droplets in supported datacenters. Enabling daily backups for a Droplet adds 30% of the Droplet's cost per month.
In more detail, each successful backup is charged at a percentage of the Droplet’s total cost that month. This means that you may be charged less than the full monthly cost in rare cases, such as when you destroy a Droplet that is less than a month old.