IP Pool Exhaustion Calculator
See how many months of addresses your pool has left.
Your numbers
Your results
Assignable addresses
Assignable addresses
—
Free now
—
Utilisation
—
Months until exhausted
—
Alert threshold (85%) reached in months
—
IP Pool Exhaustion Calculator by TheCalcTools
How the IP Pool Exhaustion Calculator works
Enter the pool prefix, current usage, reserved addresses and monthly growth.
Free addresses divided by monthly growth gives months left.
Plan expansion when utilisation passes about 85%.
The formula
Months left = (2^(32 − n) − 2 − reserved − used) / growth
Worked example
Using the default values shown in the calculator:
| Pool prefix (/n) | 22 |
|---|---|
| Addresses in use now | 700 |
| Growth per month | 40 |
| Reserved / static addresses | 20 |
- A /22 has 1,022 usable addresses; minus 20 reserved leaves 1,002.
- 302 are free and growth is 40 a month, so the pool lasts 7.5 months (utilisation now 69.9%).
Result:
| Assignable addresses | 1,002 |
|---|---|
| Free now | 302 |
| Utilisation | 69.9% |
| Months until exhausted | 7.5 |
| Alert threshold (85%) reached in months | 3.8 |
Frequently asked questions
What if growth is seasonal?
Use the busiest month’s growth for a conservative estimate.
What is the fix when a pool runs out?
Shorten DHCP leases, add a subnet, or move to IPv6.
Sources and further reading
Related calculators
More in IP & Domain Tools · All calculators
This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.