Variable - but about every two weeks. I'd love to change them more often but it's a time thing, what with the changing washing and ironing. I used to work and live in a hotel and I changed my sheets every day took the dirty off in the morning exchanged for clean and put them on fresh every night, heaven! If I won the lottery (which is unlikely as I don't do it) I would have enough fresh linen to have fresh every day and send it out to be laundered (along with all the other washing)