10/23/2026
"It takes 21 days to form a habit." You've heard it a hundred times. It's wrong, and it makes people quit.
The 21 came from a 1960 book by a plastic surgeon who noticed patients took about three weeks to get used to a new face. He never studied habits.
When University College London actually tested it, the average was 66 days, with a range from 18 to 254.
Two more findings I use with every client. Missing a single day made no real difference. And the idea that willpower runs out like a fuel tank didn't hold up when 23 labs tried to repeat it.
So stop leaning on grit. Build the habit so it survives a bad week. Swipe for how.
How long did your last habit really take to stick?
(Lally et al., 2010. Hagger et al., 2016)