How long do you keep a pc before buying a new one?

TO be honest with My PC I upgrade parts as needed. every so often I upgrade the motherboard and cpu to the latest outside that the gpu as needed for gaming.  The benefit of a PC is you donlt need to upgrade the whole thing every few years.

That's hard to answer because I build my own desktops. 12 years ago I built a system with a Core i7 920, 6gb of DDR3 RAM, and a Radeon 4830. That system still runs but now it has a 6-core Xeon x5680, 12gb of RAM, and a Radeon RX 580. I have a newer system but I still use the old x58 system. Since I learned to build and upgrade desktops, if something isn't running the way I want it to then I'll upgrade it.

For desktop computers, Things are somewhat different now because they're not Black or White compared to 15 or 20 years ago. Back then everything came with only 1 core and RAM upgrades were more limited. Nowadays you might be able to upgrade to a CPU that has more cores and some systems that are 10 years old top out at 8gb of RAM. The advent of Solid State Drives has also helped a lot. Somewhat Sadly, you can upgrade a 10 year old midrange desktop and make it run better than a Brand New Entry-Level Desktop. That goes to show how stagnate the PC hardware market was between 2011-2017.

It depends, if the one I have is running ok why change it.

I usually upgrade parts as needed, because I build my own

Generally depends on the type of system & how it's going to be used.

For Laptops, they would have a primary use cycle of 2-3 years & potentially a secondary use cycle (at reduced or more niche use) of another 2-3 years before considering replacing.  There might be a third, experimental cycle (where I might experiment with Linux or other special use stuff) while looking or AFTER getting the replacement system, but this is around the time I'm likely to pass the system to somebody else.

This is mostly due to limited upgrade potential of laptops & the graphical components have reached the end of their mainstream usage.

For Desktops, they would have at least 2-5 years of primary use with extensions depending on upgrade potential before hitting the limits of the motherboard.  Once upgrade potential limits have been reached, I'll look at replacement & head to secondary & tertiary cycles.

Once a replacement is obtained & running, I'm more willing to pass the old PC off to others (like my mother, who doesn't need a high-end system for her more casual PC usage...  or friend / neighbor that could use as they're running what's considered an "ancient" system by today's standards...  like something that's over a decade old).  As mentioned above, I'm more willing to do more experimental stuff with old PC's like trying out other OS's or use it as part of a project that doesn't require a modern system to operate.  This can usually hit about the decade mark before seriously considering recycling or discarding the system as virtually nobody is interested in it at that point (as smaller & cheaper options, like a Raspberry Pi, have similar performance levels).

You can keep a pc for 5-10 years before you buy a new one.

I personally buy a new one only when my PC becomes very slow for some activity or does not meet “recommended” requirements for any new program. If it does not show any problem and works smoothly then I may keep it for long. The last PC I replaced was about 4 years ago.

Generally until it can't run applications or games in the way you need\want it to.    Some people are going to be willing to pay $1000+ to keep super high frame rates with ray tracing, others are fine with just having a system that can play the games they want.  

about 10 years , then the pc doesnt cost as much as your software . windows 10 , $150  office another $130 per year , they stopped you owning office , virus killer $40 , then other programs like cd burning , games . all the good stuff and dont forget the $100 headphones .

I thrive in buying those computers people ditch the moment the next next big upgrade appears!