What is the best way to know when to feed or split my cells?

Answer

A quick way is to set up several flasks of the same cell type each with different starting cell numbers. Use 5-6 flasks of each starting concentration and harvest one flask each day from each culture condition. The multiple flasks for each condition are for cell counting each day for the 5-6 days of the test. and the subsequent development of a growth curve for each conditions. Try two or 4 different starting cell concentrations. Grow the cells without refeeding, If the cells reach confluency before the cell start to plateau then refeeding may not be necessary and splitting is in order. If the cell growth plateaus before the cells reach confluence then it is time to refeed and grow another couple of days.