A static IP address never changes: it is assigned to your connection permanently. A dynamic IP address is borrowed from a pool for a period and can change. Almost all home and mobile connections are dynamic.
How dynamic addresses work
Your provider uses DHCP, a system that hands out addresses on a lease. When the lease ends, or your router restarts after being off for a while, you may receive a different address. Providers prefer this because it uses a limited supply of addresses efficiently and needs no manual management. In practice many home addresses stay the same for weeks or months, so "dynamic" does not mean "changes constantly".
When a static address is useful
- Hosting a website, mail server, game server or VPN endpoint from home.
- Allow-listing your address with an employer, bank or cloud service that restricts access by IP.
- Remote access to security cameras or a NAS without extra services.
Providers usually charge extra for it, and business plans often include it. For most people the practical alternative is dynamic DNS: a small client on your router updates a hostname such as myhome.example.net whenever your address changes.
Privacy implications
A static address is a stable identifier that follows you across every site and years of browsing. A dynamic one is slightly better because it can rotate, but because many stay unchanged for long periods, do not count on it. It is also not a substitute for hiding your address: advertisers link visits using cookies and fingerprints too, so a changed address does not reset your identity.
Do not rely on restarting your router to get a new address. Some providers hand back the same one. If you need to change your address for privacy, use a VPN.
Security considerations
A static public address is a constant target for scanners, so make sure only intended services are reachable. Use the open port checker, keep your router updated and avoid exposing management interfaces.
How to tell which you have
Check your address now, again after restarting your router and a few days later. If it never changes, you may effectively have a static address, but only your provider can confirm it. Your provider's plan description or support team can also tell you.