DHCP Lease Calculator

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

About DHCP Lease Calculator

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

Worked example

With the default values below, DHCP Lease Calculator returns Renewals Per Hour of 200.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

DHCP clientsminimum 1 clients: 800 clients
Lease timeminimum 1 min: 480 min
T1 renewal pointaccepts 1–99 % of lease: 50 % of lease
T2 rebinding pointaccepts 1–99 % of lease: 87.5 % of lease
Average client online timeminimum 1 min: 240 min

Results

Renewals Per Hour: 200.0
T1 Renewal Timer: 240.0 min
T2 Rebinding Timer: 420.0 min
Renewal Rate: 0.056 requests/s
Address Held After Disconnect: 240 min

Step by step

1Values used
2DHCP Lease
3Renewals Per Hour= 200.0
4T1 Renewal Timer= 240.0 min
5T2 Rebinding Timer= 420.0 min
6Renewal Rate= 0.056 requests/s
7Address Held After Disconnect= 240 min

Assumptions and limits

The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

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.