If you routinely upgrade to the newest flagship model each year, your decision is almost automatic. On average, most folks now replace their phone every three years, since new features are evolutional rather than revolutionary. Older users tend to keep their phones longer. A recent survey showed that 55% of Gen Y users replace their smartphone every two years or less, but only 38% of Gen X users and 22% of Baby Boomer follow that pattern.

The average smartphone lithium ion battery lasts two to three years. If your battery will only hold a charge for a few hours, it’s time to replace the battery – if it can be replaced. User replaceable batteries are all but extinct. Professional replacement costs range from $45 to $95, but some replacements are so difficult that no one is willing to make the attempt.

Damaging your phone will often force a replacement.  The cost of replacing a cracked screen out of warranty ranges from $110 to as high as $300; there may be associated hidden internal damage requiring further repairs and expenses. If you’re brave enough to consider fixing it yourself, take a look at the IFIXIT website for advice and instructions. If the repairs would exceed the residual value, a new phone is in your future.

Older devices will eventually be unable to update to the current operating system software and thus become technologically obsolete. This usually is the case by or before 5 years from the manufacturing date. If your phone’s operating system is currently several years out of date, it’s time to start shopping for a new phone.

Your service plan will be your largest expense. Begin shopping by selecting a carrier that provides reliable service in your area. Larger carriers often have excellent coverage and high speed networks, but many alternative carriers piggyback on larger networks. For instance, Straight Talk and Total Wireless use the Verizon network, often offering lower rates for the same service. Carefully estimate your data usage and select the appropriate data plan; most of us overestimate requirements and overspend.

When it’s time to buy a new phone, a highly rated model can be far less expensive than you might think. If you’re switching after just a year or two, you may be able to sell or trade in your current phone. Consider all brands; Apple and Samsung may have the most recognized names, but they are not the only companies that make terrific phones. Buying a slightly older model can save hundreds of dollars and still have more features than you really need; the latest and greatest phone may feature only minor improvements. Heavy discounts pop up shortly after the new models are announced as carriers close out older models. Comparison shop rather than selecting the most convenient location; they may be selling the same product but have significantly different prices.

If you’re a new or inexperienced smartphone shopper, you can find some solid, unbiased advice at consumerreports.org, Tomsguide.com, Lifewire.com or thewirecutter.com (search for smartphones)