Subnet math, done right.
IPv4 + IPv6, subnet planner, cloud reservation notes. Paste a CIDR or share a URL.
Why this calculator
Most free IP calculators are stuck in 2010. They do basic IPv4 math and treat IPv6 like an afterthought, or skip it entirely. They don't help you split a network into subnets. They don't tell you that AWS quietly steals 5 addresses out of every VPC subnet you create.
This one does. Paste an IPv4 or IPv6 CIDR and you get the network, broadcast, first/last usable, total addresses, netmask, wildcard mask, binary breakdown, and a reverse-DNS PTR. The cloud-reservation panel shows how many hosts you actually get on AWS, Azure, and GCP after each platform's per-subnet bookkeeping.
The subnet planner takes a parent CIDR and either splits it into N equal-sized subnets, fits N hosts per subnet, or breaks it down at a fixed prefix. Output is the list of new subnets ready to copy into Terraform or an IPAM ticket.
Everything runs in your browser. The URL state is shareable: paste a CIDR, copy the URL, send it to a coworker, they see the same numbers.