Static vs dynamic IP addresses: which one do you have?

A static IP never changes; a dynamic IP is leased from your ISP's pool and can change at any renewal, reboot, or network reshuffle — and unless you're specifically paying for static, your connection is almost certainly dynamic. The distinction only matters for one class of user: anyone who needs to be reachable at a known address. This guide shows how to find out which you have, why dynamic addresses change, and the modern alternatives that make paying for a static IP mostly unnecessary.

Maintained by the ipconfig.io team · Reviewed 1 July 2026

How do I know if my IP is static or dynamic?

Take a reading now:

curl ipconfig.io

Then test the two things that shake a dynamic address loose:

1. Reboot your router (fully — power off for a minute) and check again. A new address = dynamic, case closed.
2. Check over days. Same address after a reboot proves little — many ISPs re-issue the same lease. Watch it across a week or two instead; the monitoring guide automates exactly this with a cron job and gets you an alert on change.

One honest caveat: a stable reading never proves static. Some dynamic addresses stay put for months. The authoritative answer is your ISP plan — "static IP" is an explicit, usually paid, line item. And if you're behind CGNAT, the question changes shape entirely: the public IP isn't yours alone in the first place.

Why does my public IP keep changing?

Because your ISP owns a limited pool of addresses and leases them out via DHCP. The lease model is cheaper to operate, lets the ISP rebalance its network freely, and — since IPv4 addresses are scarce and cost real money — lets one pool serve more subscribers than a permanent one-address-per-customer scheme would.

Typical change triggers, roughly in order of frequency:

Trigger	Typical on
Lease renewal at ISP-set intervals	DSL, cable, fiber
Router or modem reboot	Everything
ISP maintenance / network rebalancing	Everything
Every reconnection	Mobile data, many CGNAT ISPs

Do I need a static IP?

Decide by one question: does anything need to reach you at a known address?

• Yes — you self-host a server, game server, VPN endpoint, or camera DVR; you need your home in an office allowlist; you run services with DNS records pointing at your connection. You need address stability.
• No — you browse, stream, game as a client, work remotely via normal apps. Dynamic is fine. It's also free, and marginally more privacy-friendly: a rotating address is a weaker long-term identifier for the trackers that log it (what an IP exposes).

Even in the "yes" case, a paid static IP is no longer the default answer:

• Dynamic DNS (DDNS) — a client updates a hostname whenever your address changes, so home.example.com follows the moves. Free tiers abound; pairs with the monitoring cron.
• Tunnels — Cloudflare Tunnel, Tailscale, WireGuard to a small VPS: your service connects out to a stable endpoint, so your home address never needs to be reachable (and works behind CGNAT, where port forwarding is impossible).
• Paying the ISP — still the right call for allowlist requirements and anything where a bare, stable, inbound-reachable address is the spec.

Frequently asked questions

What's the difference between static and dynamic? Static is permanently assigned and never changes; dynamic is leased from a pool and changes on renewals, reboots and reshuffles. Home connections are almost always dynamic.

How do I know which I have? Reboot the router and compare curl ipconfig.io before and after; watch it over days. Only your ISP plan gives a definitive answer — stability alone doesn't prove static.

Why does my IP keep changing? DHCP leases: renewals, reboots, maintenance, and constant remapping on mobile and CGNAT connections.

Do I need a static IP? Only if something must reach you at a known address — and DDNS or an outbound tunnel usually solves that without one.

Next steps

• Monitor your public IP for changes — the cron-based watcher that answers "did it change?" for you.
• What is CGNAT? — when the public IP was never exclusively yours to begin with.
• Find your public IP from the terminal — every way to take the reading this guide starts from.