My Scientific American column this month pondered the possibility that tech companies deliberately withhold features that are ready to go into their products, simply so that they’ll have something more to entice you with next year.

And it’s true that technology moves so fast, almost any gadget you buy will soon seem behind-the-times. To avoid the feelings of betrayal and waste that accompany the discontinuation of whatever you bought, it’s best to keep its limited lifespan in mind from the day you start shopping.

It also helps to know when electronics are likely to go obsolete. As it happens, certain products come out at about the same time every year. If you pay attention, you can avoid the sinking feeling that comes from buying a new phone or tablet only a month before a better model replaces it.

Here’s a rough schedule:

iPhones: Apple releases a new iPhone model every year. For the first few years, that big event was in July; these days, it’s early October. In other words, if you worry about obsolescence, don’t buy a new iPhone in September.

Samsung Galaxy S phones: These popular iPhone rivals (now up to version 4) have hit the market in May each year. You’ve been warned.

Digital cameras: There are two big international camera trade shows, where the Canons, Nikons and Sonys of the world unveil their newest models: February and October. Hope you didn’t get too attached to the camera you just bought six months ago.

iPads: The first three iPad models came out in March. When the fourth-generation model came along, though, it popped up in November, which suggested that Apple is trying to swing its annual releases around to the holiday season.

Everything else: TVs, GPS units, laptops—other companies and other industries march to the beats of all kinds of different drummers. If in doubt, keep your eye on September and October. A great majority of the electronics companies time their new releases to land at the beginning of the holiday shopping season; if you’re keen to get the latest new thing, you’ll follow their lead.