I probably do about every three years because I want a new look.

I like to get at least a coverlet which only costs $20-30 every year. Missed doing that the last couple years & got a couple last month. But for something pricier every 2 or 3 years probably.

We get a new comforter cover every couple of years or so.

We have a king sized bed and prices of bedding are king sized as well. Then those velour blankets that seem to be preferred now we don't like. So the blanket we are using is probably 10 years old. I did buy a 100% wool blanket at a yard sale some years ago, it is still in perfect condition so when the old one gives up the ghost we still have the wool one.

I have this old knappy light blue blanket that used to be one of those soft fuzzy things when you buy it. It is just the right thickness for me to be comfortable in an air conditioned room, so I have never tried to replace it. A new one would probably be too warm. IDK how long I have had it, forgot when I got it.

I buy bedding often enough. Whenever I see something I like, I'll get it.