The frequency with which you need to replace a modem can vary depending on several factors, such as the quality of the modem, technological developments, and personal needs. In general, a modem can last for several years before it possibly needs replacement. Here are some considerations:

1. Technological developments: Internet connection technologies and standards can evolve and improve. For example, if you have an older modem that is not compatible with the latest technologies, such as faster internet speeds or more advanced security protocols, it may be necessary to upgrade to a new modem.

2. Changes in internet needs: If your internet needs change over time, a new modem may be required to meet those needs. For example, if you originally had a lower internet speed but now need more bandwidth for streaming, gaming, or working from home, a new modem with higher speeds may be required.

3. Reliability and performance: Over time, modems can wear out and become less reliable. If you notice that you regularly experience problems with your internet connection, such as outages or slow speeds, it may be time to replace your modem.

It's advisable to regularly stay in contact with your internet provider and inquire about any modem upgrades or recommendations. They can guide you in determining the optimal lifespan of your modem and when it's time to upgrade based on your specific situation.