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DHCP Lease Calculator

Work out DHCP T1 and T2 renewal timers and the renewal load a client population puts on the server.

Inputs

clients
min
% of lease
% of lease
min

Renewals Per Hour

200.0

T1 Renewal Timer

240.0min

T2 Rebinding Timer

420.0min

Renewal Rate

0.056requests/s

Address Held After Disconnect

240min

Step by step

  1. Values used

    DHCP clients = 800 clients; Lease time = 480 min; T1 renewal point = 50 % of lease; T2 rebinding point = 87.50 % of lease; Average client online time = 240 min

  2. DHCP Lease

    T1 = lease × 50%, T2 = lease × 87.5%, and renewals per hour = clients × 60 ÷ T1 in minutes.

  3. Renewals Per Hour

    = 200.0

  4. T1 Renewal Timer

    = 240.0 min

  5. T2 Rebinding Timer

    = 420.0 min

  6. Renewal Rate

    = 0.056 requests/s

  7. Address Held After Disconnect

    = 240 min

How it works

RFC 2131 has clients renew at half the lease and rebind at seven-eighths of it, so each client generates one renewal every T1 minutes regardless of whether anything changed. Any lease longer than the client's session leaves the address reserved after it disconnects. Halving the lease time doubles server request load and doubles the churn in DNS if you run dynamic updates, while very long leases silently strand addresses in a busy guest network.

Formula

DHCP Lease

T1 = lease × 50%, T2 = lease × 87.5%, and renewals per hour = clients × 60 ÷ T1 in minutes.

T1
When the client first tries to renew with its current server
T2
When the client gives up and broadcasts to any server
lease
Total lease duration

Frequently Asked Questions

How is DHCP Lease calculated?

T1 = lease × 50%, T2 = lease × 87.5%, and renewals per hour = clients × 60 ÷ T1 in minutes. RFC 2131 has clients renew at half the lease and rebind at seven-eighths of it, so each client generates one renewal every T1 minutes regardless of whether anything changed. Any lease longer than the client's session leaves the address reserved after it disconnects.

Why does DHCP Lease matter?

Halving the lease time doubles server request load and doubles the churn in DNS if you run dynamic updates, while very long leases silently strand addresses in a busy guest network.

What values do I need to enter?

This calculator takes 5 inputs: DHCP clients, Lease time, T1 renewal point, T2 rebinding point, Average client online time. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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