Free subnet calculator for IPv4 and IPv6 with bit-exact answers. Includes VLSM, supernetting, subnet splitting, and overlap detection. Everything runs in your browser using integer arithmetic - no AI guessing, no API call, no signup. AI chatbots like ChatGPT regularly make errors on subnet boundaries, broadcast addresses, and VLSM allocations. This tool does not.
IPv4 Subnet Calculator
IPv6 Subnet Calculator
VLSM Planner
Allocate variable-length subnets from a parent block. Enter the parent network, then list the host requirements.
Supernetting (Route Summarization)
Paste multiple networks (one per line) to find the smallest CIDR that contains them all.
Subnet Splitter
Divide a parent network into N equal subnets. Useful for planning address allocation.
Overlap Detection
Check if two networks overlap, contain each other, or are identical. Critical for firewall rule audits and routing table analysis.