As a Network Engineer, I have replaced a lot of modems. And let me say, they last longer than you would expect.
Often, people change modem without needing to, in hopes of getting a faster internet connection. But you will never get faster internet than your plan.
Therefore, I have written this guide on how long a modem lasts, and when you should replace it.
Let’s get started.
The Average Lifespan of a Modem
A modem usually lasts between four to seven years, while a modem/router combo (or gateway) lasts about three to four years.
This is against a lot of what you find online, which often promotes changes earlier than necessary. Even many Internet Service Providers will recommend changing a modem every 3 years or so.
There are, in fact, only a couple of reasons why you should replace your modem. These are:
- The modem breaks or you have problems with it, and your warranty has expired.
- You have changed ISP, and it’s not compatible with your new internet.
- You have upgraded your internet plan, and your modem is incapable of handling the new speed.
- If you pinpointed that the modem is the cause for a slow internet connection.
- If you add a special service that your existing modem doesn’t support, like VoIP, for example.
Below you can learn about them in more detail.
Reasons You Should Consider Replacing Your Modem
Like most pieces of technology, a modem doesn’t last forever. Several factors contribute to when your modem’s functionality begins to waver.
Despite the differences between each modem model, they all perform similar tasks when accessing the internet. Consider these scenarios when asking yourself, do I need a new modem
#1 It Breaks or Experiences Problems, and Its Warranty Has Expired
Most modems have a one to two-year warranty if you accidentally break it or it starts malfunctioning frequently. Overheating, dust, and power disruptions can cause your modem to wear down.
Once the warranty expires, the modem’s manufacturer won’t fix or replace it. Then the best course of action is to simply get a new modem.
#2 Your Modem Isn’t Compatible with Your New ISP
Every ISP has a list of approved modems for their internet. So, if you change ISP and your modem isn’t on their list. Then it most likely won’t work for your internet.
This will most often happen if you change the type of internet, like from DSL to cable. Because no DSL modem works for cable internet. 
But even if you change between cable providers, you sometimes need to get a new modem.
If this is the case for you, then I would recommend checking out the certified modems page. There you can find lists with ISP-approved modems.
#3 Your Modem’s Speed is Too Slow for Your Upgraded Internet Plan
Another reason you need to replace your modem is if you have an unbalanced speed between your device and your updated Internet plans.
Suppose you upgrade to a 400 Mbps plan to increase your Internet speed.
If you have a modem that only is capable of 200 Mbps, then that will be your max speed.
Even though your plan is 400 Mbps.
#4 Your Modem Causes Slow Internet Connection
If your modem is supposed to be able to support your speed. But for whatever reason isn’t and is, therefore, causing a slow connection. Then you need to change it.
If you are uncertain if it’s the modem that causes your slow internet, try connecting a computer directly to it and run a speed test.
#5 Adding a Service That Your Old Modem Doesn’t Support
Some special Internet services, such as VoIP applications necessitate modems with eMTA. Something ordinary cable modems don’t have. 
Therefore, if you add this service you will need a new modem.
Often, however, your ISP will give you such a modem for free. Because most ISPs don’t have any third-party approved modems with eMTA support for sale anywhere.
There are expectations, like Comcast Xfinity, for example, that enables third-party approved modems.
What About Gateways?
Although many of the reasons for replacing a modem might apply to modem/router combos, there are other factors you should consider that might be exclusive to them.
You’re more likely to frequently replace a gateway than a standalone modem due to its router characteristics.
Another factor that affects your gateway’s lifespan is its signal strength. A gateway’s signal strength weakens over time.
Due to this factor, gateways have shorter lifespans than traditional modems.
The lifespan for modems is often up to seven years, while a gateway only lasts for about four years.
Gateways don’t upgrade as frequently as modems, making them more prone to getting replaced. 
Although there are several advantages of using a gateway, you should monitor its activity to determine when you’re ready to replace it.
Modems are reliable pieces of technology. But as technology advances, older models might not be suitable for high-speed Internet connections.
When issues begin occurring with your modem or gateway, it would be wise to consider replacing it.
Most modems last about four to seven years, while gateways last between three or four years.
The rate you replace them depends on your Internet connection’s quality and how your modem handles it over the years.
Although many modem manufacturers, ISPs, and online resources recommend replacing your devices earlier than necessary, keeping them for at least four years might be more convenient for you. I recommend monitoring your modem to ensure you don’t replace it too soon.
If you think you need to get a new modem and want some help finding a replacement, browse through this list of modems that are compatible with your ISP.