A landmark study by researchers in the UK found that simple health habits, such as eating a piece of fruit with lunch or running for 15 minutes before dinner, took an average of 66 days to form. Behavioral researchers say two to three months is a safe bet on average, but the more complex the behavior, the more difficult it is going to be to put on autopilot.

Recent research is uncovering how long it takes to cement different kinds of habits—and gives fresh insight into how to make them stick. According to a recent study, simple health habits like handwashing, for instance, take a couple of weeks to develop, while more complicated ones like going to the gym take four to seven months. “You can’t mindlessly go to the gym the way you mindlessly shampoo your hair,” says Katy Milkman, co-author of the study.

One big lesson if you’re trying to establish a new healthy habit: You will have better luck if you can simplify the process and repeat it often. Finding ways to make it fun and setting realistic expectations about how long it will take to establish the habit will help too.