Your going to have a huge argument here because there are so many variable depends on type of fish, number of fish, and how many gallons. Basically how much and how quickly waste accumulate in the given amount of water will be different for everyone. I see people on here that do 70% water changes every other day. I am hoping that is an exaggeration otherwise it is wasteful and irresponsible. Some say they do it once a week others do it once a month I think both are right depending on there fish.
On one of my tanks I do 50% every two weeks on my other two tanks I do 50% every month. The ones I do monthly do have more algea but not to much my main display tank that I do every two weeks has no algea. Both tanks test fine as far as water quality.