Is my network data sent to a server?

No. The whole calculation is done in your browser with plain JavaScript bitwise math. No IP address or network detail ever leaves your device.

Why are usable hosts two fewer than total addresses?

In a normal subnet the first address is reserved as the network address and the last as the broadcast address, so they cannot be assigned to hosts. The /31 and /32 prefixes are special cases handled accordingly.

What is a wildcard mask?

A wildcard mask is the bitwise inverse of the subnet mask. It is used in tools like access-control lists to specify which bits of an address can vary, and the calculator derives it automatically.

IP Subnet / CIDR Calculator

Work out network, broadcast, host range and mask from any IPv4 CIDR.

IP subnet and CIDR calculator

Enter an IPv4 address in CIDR notation — for example 192.168.1.10/24 — and instantly get the network address, broadcast address, usable host range, subnet mask, wildcard mask, and total address count.

All of the math is bitwise arithmetic done in your browser, so no address or network detail is ever uploaded.