How long you you keep your iPhone?

I buy a new phone when the main updates are no longer supported by Apple for the old phone, or if it just doesn't work anymore, and isn't practical to have it repaired etc. Then I use the old phone for a few weeks as if it were an iPod. But then I realize it's just easier to do all that on the new phone, and that the old phone's battery is horrible, and shut it completely down. Then it just sits there until I remember to charge it because it still loses charge for what ever reason. It's kind of that way with all my devices and other technology, unless I can scavenge something for parts, like hard drives etc. Never know when you might need a flywheel and capstan out of an eight-track player or something...

I got the 13 pro last Nov. When I finished paying this, I will get the 15 pro

I don't buy them new either, that is highway robbery; I buy refurbished, usually a year old. My last phone is an 8, and I still use it for a couple of functions, it is six years old and still getting updates.

Usually, I try to keep my devices until they stop receiving major OS updates which is usually 5 to 6 years. Keep in mind that Apple has lately offered security patches to older iOS devices for an additional 2 to 3 years. For example, the iPhone 6s is still receiving security patches for iOS 15, and we're now a little over 8 years since the device was released. The iPhone 5s received updates until January 2023 which is extremely impressive!
having said that, my sister constantly gets new phones, which I find extremely wasteful. As I write this, I'm using an iPhone 11 and have an 8, 6s, and my old 5s in a drawer next to me. I want to get the new SE when it launches, because I'm tired of getting used devices with damaged microphones and speakers. I hate planned obsolescence! Fortunately, Apple is now providing very good long-term support.

When software can no longer be upgraded, it's time for a new phone. Recently, though, I've been thinking more about getting a new phone every year. I'm tempted by how much I can get for treading in last year's phone. Presently, I have an iPhone 10s, but day after tomorrow I'm receiving an iPhone 15 Pro in the mail. Smile. Wish me luck!

Certainly some approaches here. I know of people like here in the comments who use a phone until it dies. The battery can make it die though sooner than it should.
It can also depend on available trade in options in your area. I find for myself, since I prefer new when I do upgrade, that every two years is the sweet spot for trade-in value to Apple. I am trying to do better about trading off old stuff instead of keeping it where it ends up in a drawer and isn't used anyways. I'd say I am the best at trading phones.
Anyhow, no matter how you slice it, iPhone is not the cheapest thing to own.

I usually keep my stuff for as long as they can serve me. My old SE 1st generation was retired only this year, replaced by a 13. I'll keep it until it isn't updated anymore or when it has some serious hardware issue which makes it impossible to use. I can't afford an iPhone each year and, to be honest, new iPhones usually aren't worth the spend.

I am keeping my Apple gear until it doesm't work, than ditching Apple entirely, Android and windows are so much more practical because you can easaley replace the OS. when newer versions of windows come out, you can upgrade, unless Microsoft changes system requirements. in that case, Linux is opensource and always free, and it runs on every computer. Android can be rooted and flashed, and I can't wait 'till my iPhone dies, so I can flash the most current version of Android through a custom rom, on my Nexus 6. at one time, Apple were the only game in town for built-in screen reading, but these days, NVDA is just as good as VoiceOver, can ve scripted more universally, and just as capable. maybe even more so wiith add-ons.

I got an iPhone 7 just before Easter 2018, and that is what I'm using to this very day. My parents tell me that upgrading to one of the newer iPhones will be rather costly, even with the family plan that I'm on. However, I am going to try and convince them to let me upgrade. This is due in large part to me needing to live a healthier lifestyle, and I therefore need an iPhone with a bigger camera so that I can scan/take pictures of what I am eating and drinking. There are of course other factors which are contributing to my decision, but based on what I currently know health is key here. But I guess we'll just have to wait and see what happens on that front. The iPhone 7 which I currently own has been awesome though, and I heartily commend Apple and others on a job well done. These things are most certainly worthy of an award of some kind.

I agree with Daniel, though I want to keep at least one foot in iOS land for a variety of reasons. My primary mobile phone is now a Pixel and it's great, but I find I use my iPhone 11 very frequently too. Having access to both platforms gives you the best of both worlds, and Apple's long-term support means my iPhone isn't immediately obsolete.
As for Windows 11 system requirements, they're very easy to bypass if you're comfortable doing some tweaking, just like loading newer versions of Android onto unsupported devices. It's a shame you can't do this with iOS, but iOS isn't meant for the extreme power user, and of course Apple wants to make money. I'll get the new SE when it launches which will allow me to stick around in iOS land for a little while longer to continue enjoying apps like Seeing AI and Timecrest. I wish the ipod Touch was still around, because it would be perfect for my ideal use case. I don't want an ipad because the screen is too big, so I'll have to deal with using an iPhone like an iPod Touch.

Ekaj, you may want to consider the new SE when it arrives. It's significantly cheaper than the modern flagship phones, and I think you'll be very pleased at the performance boost. I expect the device to come with the A16 or A17 chip, so you should notice a dramatic difference compared to the A10 in your current phone. You'll also be able to take advantage of the new VoiceOver AI features, though I personally don't find them as useful as I'd like them to be. Of course, they may improve in the future, hence why having newer hardware is always to your advantage.

I might keep this one for a bit longer as the newer phones have nothing for me to be excited about.

My mother actually offered to take me to Best Buy and have them replace the battery, but I really want to take advantage of the new VoiceOver features if at all possible.

Both my wife and I keep our iPhones until a new model offers something we want that our current phones don't have. For instance, I upgraded to my current iPhone, the SE 3rd generation with 256 GB storage, from an iPhone 8 with 64 GB of storage. I don't plan to upgrade again for a while. My wife just upgraded her iPhone 11 Pro Max to the iPhone 15 Plus with 256 GB storage because her iPhone 11 only had 64 GB of storage and she needed more. Also, she got the new iPhone 15 Plus for free from our carrier (T-Mobile) with a trade-in of her iPhone 11. In other words, we don't necessarily keep our phones until they are out of support, but we don't upgrade every year or two either.