Why does your public IP keep changing? DHCP leases explained

Quick answer

If your public IP is different every few days — or every time you restart the router — that’s a dynamic IP doing exactly what it’s designed to do. The mechanism behind it is the DHCP lease. Here’s how it works.

DHCP and the lease concept

Your ISP assigns your public IP via DHCP (Dynamic Host Configuration Protocol), which hands out addresses on a lease — a temporary assignment with an expiry. When the lease ends, your connection renews it, and the ISP may give you the same address or a different one from its pool. Short leases mean more frequent changes.

What triggers a change

Your IP can change when: the DHCP lease expires and renews with a new address; your router reconnects after a reboot or outage; your connection sits idle long enough for the lease to lapse; or the ISP reorganises its address pool. None of these is a fault — it’s normal dynamic behaviour.

Why do ISPs use dynamic IPs?

Dynamic assignment lets an ISP serve more customers than it has addresses, since not everyone is online at once — an efficient use of scarce IPv4 space. It’s cheaper to operate and slightly better for customer privacy, since your address isn’t a permanent identifier. That’s why dynamic is the default and static usually costs extra.

“Sticky” dynamic IPs

Many dynamic IPs are sticky — technically dynamic, but you keep the same address for weeks or months because the lease keeps renewing to the same value while you’re continuously connected. So “dynamic” doesn’t mean “changes constantly”; it means “can change.” A long stable period followed by a sudden change is typical.

Watching it happen

Our homepage IP history log records each address it sees, so you can observe your own lease behaviour over time. If you need a constant address despite the changes, the options are a static IP from your ISP or Dynamic DNS to track the changing one.