Why does my IP change?
Your address is borrowed, not owned. Here is what makes the tide turn.
Dynamic and static, and why yours is dynamic
Addresses come in two flavors. A dynamic address is lent to you for a while and can change. A static address is assigned permanently and does not.
Almost every residential and mobile connection is dynamic, and that is a deliberate choice by providers rather than an oversight. Dynamic assignment lets a provider hold fewer addresses than it has customers, because not every customer is connected at once, and it lets them reorganize their network without visiting anyone's house. Static addresses are usually a business plan feature and usually cost extra.
How a lease actually works
DHCP, the Dynamic Host Configuration Protocol, is what hands out addresses. When your equipment connects, it asks for an address, and a server responds with one plus a lease time: how long that address is yours.
The part people miss is that a lease is renewed long before it expires, and a renewal normally returns the same address.
So the honest answer to "why does my IP change" is not that it changes constantly. It is that the renewal cycle can be interrupted, and when it is, the next address you get may be a different one.
What actually interrupts the cycle
| Trigger | How likely it changes your address |
|---|---|
| Rebooting the router briefly | Low. The lease is usually still valid and gets renewed |
| Router off for hours or days | High. The lease expires and the address returns to the pool |
| An extended outage on the provider's side | Moderate to high, depending on how long it lasted |
| Provider maintenance or renumbering | High, and there is nothing you can do about it |
| Swapping the router or modem | High. Different hardware often means a different lease |
| Connecting somewhere else | Certain. A different network means a different address |
| Toggling airplane mode on a phone | High. Mobile addresses are the most volatile of all |
They are separate address spaces handed out by separate mechanisms. Your IPv4 address can change while your IPv6 address does not, or the reverse. If you are tracking one, do not assume the other followed it.
Mobile networks are a different animal
On a cellular connection the address can change while you are sitting still. Carriers manage enormous shared pools, and your address can move when you hand off between towers, when the device idles and reconnects, or for no reason you will ever observe.
Most carriers also place customers behind carrier-grade NAT, where thousands of subscribers share one public address at the same time. Quite the crowded pod. That is also increasingly true on fixed-line connections, because providers ran out of addresses to give every customer one.
How to tell if you are behind it
Open your router's status page and find its WAN or internet address, then compare it to the address on our front page.
- They match. You have a normal public address, and port forwarding can work.
- The router shows
100.64through100.127. That is the reserved carrier-grade NAT range. You are sharing an address, and port forwarding cannot work. - The router shows a private range and they do not match. There is another router or a modem in gateway mode between you and the internet. That is double NAT, and it has the same practical effect.
What to do when something needs a stable address
Usually this comes up because a vendor asked for an address to put on an allowlist, or because you want to reach something at home from outside. There are three real answers and one that sounds right but is not.
Ask your provider for a static address
The direct answer. Common on business plans, sometimes available on residential ones for a monthly fee. It is the only option that gives you an address nobody else will be handed.
Use dynamic DNS
A dynamic DNS service gives you a fixed hostname that follows your changing address. A small client on your router or a machine at home reports the current address whenever it moves. Anything that accepts a hostname rather than a raw address works with this, and it costs nothing or nearly nothing.
Route through something that already has a fixed address
A VPN with a dedicated address, or a small cloud instance you connect out to. Your traffic then leaves from an address you control regardless of what your provider does at home. This is also the only one of the three that works under carrier-grade NAT.
Giving a vendor your current dynamic address and hoping. It will hold for days or weeks and then stop, and the symptom will be a confusing authentication or permission error rather than anything that says "your address changed." If you have already done this, that is worth knowing before it fails at an inconvenient moment.
Can I force a change?
Sometimes, and less reliably than the internet suggests. Powering the router off long enough for the lease to lapse is the usual advice, and it works often enough to be worth trying, though "long enough" depends on a lease time you cannot see. Changing the device that requests the lease can also do it.
What will not do it is anything inside your own network. Restarting a laptop or changing its private address has no effect on the public one, because the public address belongs to the connection rather than to any device on it.
If the goal behind the question is privacy rather than a technical need, an address change is a much smaller step than it sounds. Cookies, logins, and browser fingerprints all survive it.