The procedure seems to clear the head and stops people worrying or over-thinking when they get into bed, researchers have discovered.
It works better than another approach of writing down everything that has happened that day.
It seems counter-intuitive because thinking about what has to be done the following day might be expected to increase worry—but it doesn't, say researchers from Baylor University's Neuroscience and Cognition Laboratory.
They tested both approaches on a group of 57 university students, who were given five minutes before going to bed to either write about the day that had passed or what they had to do the following day.
Monitoring brain activity once the students were in bed, the researchers found that those who wrote down a 'to-do' list slept more deeply and for longer. "Writing a 'to-do' list seems to offload thoughts and reduce worry," said lead researcher Michael K Scullin.
Around 40 per cent of adults suffer some problems falling asleep at least a few times a month. Although none of the students were insomniacs, Dr Scullin thinks the practice could help those who are.