DHCP Range Calculator

What a DHCP range is

A DHCP range (pool) is a contiguous block of IPv4 addresses that a DHCP server leases to clients — laptops, phones, printers, IoT. On a router or DHCP server you typically set a start and end address (or start + count). This calculator derives start and end from the subnet (IP/CIDR) plus an optional reservation of the first usable hosts.

The pool is not the whole subnet. Network and broadcast (on a classic LAN) must not be leased. Gateway, DNS servers, domain controllers, and network printers usually stay outside the pool — either as MAC reservations or as exclusions before the pool start.

DHCP range vs usable host range

• Usable host range — on a classic LAN, every address between network and broadcast (e.g. 192.168.1.0/24: .1–.254, 254 hosts).
• DHCP range — a subset of usable hosts the server may assign. Often narrower: keep the low end for gateway/static, use the middle or high end for DHCP.
• Reservation in this calculator — skips the first N usable addresses from the network side. Reservation 1 on a /24 usually means: gateway .1 outside the pool, pool from .2.
• MAC reservations — a separate server feature: a client always gets the same IP (often still inside the pool). Do not confuse with the form’s “reserved hosts”.

Example: usable 192.168.10.1–254, but DHCP pool .100–.199 (100 addresses). .1–.99 and .200–.254 stay for static / future use. This tool models “pool from first usable after reservation through the last usable.” For a mid-block pool (.100–.199), confirm the CIDR here, then set start/end manually on the router using the home example below.

How to choose start and end

• Count devices — concurrent DHCP clients plus 20–50% headroom for guests, phones, and new IoT.
• Protect infrastructure — typically keep .1 (or the first few) out of the pool; servers often live in .2–.20 or another VLAN.
• Avoid neighbor VLAN overlap — start and end must sit inside the same CIDR. Cross-check with the subnet calculator.
• Lease time vs pool size — short leases (1–4 h on guest Wi‑Fi) stretch a smaller pool; long home leases (1–7 days) need enough addresses for stable devices.
• Document it — record CIDR, gateway, DHCP pool, and static range in VLAN notes — speeds up IP-conflict troubleshooting.

Home /24 example (.100–.199)

Network: 192.168.1.0/24. Usable hosts: .1–.254.

• Gateway / router: 192.168.1.1 (outside DHCP).
• Static (optional): .2–.20 — NAS, printer, Pi, cameras.
• Typical DHCP pool: 192.168.1.100–192.168.1.199 → 100 addresses for laptops, phones, TVs, guests.
• Headroom: .200–.254 for future static or a second pool.

In this calculator, 192.168.1.0/24 with reservation 1 yields .2–.254 (wide pool). If your router only accepts start/end, enter .100 and .199 from the plan above — the CIDR and usable-host counts still verify that the plan fits in /24.

Quick check: enter 192.168.1.50/24, reservation 1 — network should be 192.168.1.0/24, pool start .2.

Small office / VLAN example

Staff VLAN: 10.20.30.0/24. L3 gateway: 10.20.30.1. Printers/scanners: .5–.15 (static). DHCP on the controller/firewall.

• Calculator reservation = 15 → pool 10.20.30.16–10.20.30.254 (239 addresses) when static occupies the low end.
• Or a tighter pool: .50–.200 (151 addresses) with slack on both ends.
• Separate guest VLAN (10.20.40.0/24) with its own DHCP pool and isolation — do not mix guests into the staff subnet.
• In a VPC the same idea applies: subnet CIDR + cloud DHCP options; plan how many IPs are for ENIs vs ephemeral clients.

/26 office slice: 10.0.5.0/26 → 64 addresses, 62 usable. Reservation 2 (gateway + jump host) leaves 60 pool addresses — fine for a small branch, tight if you add many IP scanners.

When the subnet is too small (/30, /31, /32)

• /30 — 4 addresses, 2 usable. Typical point-to-point link. DHCP almost never makes sense; both IPs are usually static.
• /31 (RFC 3021) — 2 addresses, both usable on P2P. No classic network/broadcast pair. DHCP here is atypical; the result shows a special note.
• /32 — single host / host route. No DHCP pool.
• /29–/28 — small DMZ or lab (6–14 usable). DHCP is possible, but reservation 1–2 eats the pool quickly — count carefully.

If the calculator warns or returns an empty pool, do not force DHCP — enlarge the subnet (e.g. /30 → /29) or use static addressing.