If you're currently renting a cable modem, check your monthly bill for the rental fee. Comcast, Cox, Optimum, and Spectrum (formerly Time Warner Cable or Charter, depending on your region) all charge fees, though this can depend on your plan. Cox offers a free modem if you bundle a TV, internet, and digital phone plan, for example.

If you have a fee on your bill, you could save between $60 and $120 per year by buying your own modem instead of renting. Sure, you'll have to pay more up front—most modems cost between $50 and $100—but within a year, you'll have recouped the cost of those fees, and you'll begin saving $10 a month. That adds up over time. Just be sure your cable company actually stops charging you the rental fee, since they've been known to "forget" in the past.

Also keep in mind that many ISPs rent modem/router combo units. We generally recommend keeping these two devices separate, so we'll just be discussing modems in this guide. If you don't already have a wireless router, you'll need to buy one of those too, which can bring up the cost of upgrading (though you'll still be better off in the long run—especially if you need a mesh Wi-Fi system to reach the furthest corners of your house).

There are some benefits to renting, though. When you rent a modem, you can trade it in when it becomes obsolete or if it stops working. Plus, you don't have to worry about compatibility or replacing the unit yourself if something goes wrong—instead of troubleshooting problems on your own, your ISP can just swap it out for you. Some ISPs include the cost of a modem in your package pricing too, and in those cases, you won't save any money by purchasing your own.

In addition, some ISPs may not even let you buy your own modem. If you have DSL or fiber, you can't use a cable modem; each uses special equipment that you'll have to rent or purchase from your ISP. In addition, if you bundle your home phone service with your internet plan, you'll need a modem that has a phone port.

Telephony modems aren't widely available for sale—a quick search yields expensive products with outdated technology—so you're most likely better off renting from your ISP. Again, if you're in a region covered by Cox, you can get a free modem if you bundle services.

If you aren't sure what you're allowed to do, check your ISP's website, or give customer service a call to see if it's possible to use your own modem. Most will list compatible modems on their website (here are the lists for Comcast, Cox, Spectrum, and Optimum).