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.
Frequently Asked Questions
How does Subnet Calculator work?
Free subnet calculator for IPv4 and IPv6. Bit-exact CIDR, VLSM, supernetting, overlap detection. No signup. AI cannot reliably compute subnets - we do. Everything runs locally in your browser for instant results and maximum privacy.
Is my data private when I use Subnet Calculator?
Yes. Subnet Calculator runs entirely in your browser using client-side JavaScript. Your input is never uploaded to any server, never logged, and never shared. Closing the tab clears everything from memory.
Do I need to sign up or create an account to use Subnet Calculator?
No. Subnet Calculator is 100% free with no signup, no email registration, no payment, and no ads. Open the page and start using it immediately.
Does Subnet Calculator work without an internet connection?
Subnet Calculator must reach public authoritative servers (DNS resolvers, WHOIS, certificate transparency logs, or exchange APIs) to fetch live data, so it requires an internet connection for live queries. Browser-based processing itself runs locally.
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