Floating IPs are free when assigned to a Droplet.
Due to the shortage of IPv4 addresses available, if you reserve an address but don’t assign it to a Droplet, we charge $0.006/hour. You will not be charged unless you accrue $1 or more.
Floating IPs are available in all datacenters. They are region-specific resources and can only be assigned to Droplets within the same datacenter.
Floating IPs let you redirect network traffic between any of your Droplets within the same datacenter. With Floating IPs, you can create highly available server structures without a single point of failure.
By default, you can reserve three Floating IPs per account. If you reach this limit, you can request more through the Control Panel interface.
A Droplet must have an anchor IP before a Floating IP can be assigned to it. Droplets created after October 20, 2015 automatically have an anchor IP, and you can create an anchor IP on older Droplets.