Check whether a DHCP pool has enough addresses once lease overhang and growth headroom are included.
A lease that lasts longer than a client's session keeps the address bound after the device leaves, so the pool has to cover the overhang as well as the live population. The ratio of lease time to session time is exactly that multiplier. This is the arithmetic behind almost every guest-Wi-Fi outage: a /24 with an eight-hour lease and two-hour sessions supports only about 60 concurrent devices, not 250.
DHCP Pool Capacity
addresses required = peak clients × (lease time ÷ average online time) × (1 + growth).
Usable pool size
pool size = 2^(32 − prefix) − 2 − reservations
addresses required = peak clients × (lease time ÷ average online time) × (1 + growth). A lease that lasts longer than a client's session keeps the address bound after the device leaves, so the pool has to cover the overhang as well as the live population. The ratio of lease time to session time is exactly that multiplier.
This is the arithmetic behind almost every guest-Wi-Fi outage: a /24 with an eight-hour lease and two-hour sessions supports only about 60 concurrent devices, not 250.
This calculator takes 6 inputs: Subnet prefix length, Static and infrastructure reservations, Peak concurrent clients, Lease time, Average client online time, Growth headroom. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.