Subnet Calculator

Enter an IPv4 address and a prefix — everything else follows immediately: network address, host range, masks and the bit boundary between network and host portion.

Notes

Runs in your browser. The calculation happens entirely on your device. Nothing you type is transmitted, stored or analysed.
The /31 case. Under RFC 3021 there is no network or broadcast address — both addresses are usable. Intended for point-to-point links.
The /32 case. Describes exactly one address. Common for loopback interfaces and single host routes.