Backups are automatically-created disk images of Droplets. Enabling backups for Droplets enables system-level backups at weekly intervals, which provides a way to revert to an older state or create new Droplets.
Enabling backups for a Droplet adds 20% to the cost of the Droplet.
In more detail, each successful backup is charged at 5% of the Droplet’s total cost that month. This means you may be charged less than 20% in rare cases, like when you destroy a Droplet that is less than a month old, but you will never be charged more than 5% of the Droplet’s monthly cost per backup.