Bedtime Calculator

How it got there

The rule

One linear rule per age. D is how long a child of this age is awake on a no-nap day, bed to bed. A nap pushes bedtime later by only a share k of its length (measured: about half in toddlers, a quarter in preschoolers), and a nap taken earlier or later than usual moves bedtime by a share m of that displacement. She cannot settle before a minimum awake stretch after the nap. Nothing is capped; anything unusual shows up as a note.

Where the numbers come from

• Guidelines (AASM 2016, NSF 2015): 11 to 14 h of sleep per 24 h at 1 to 2 years, 10 to 13 h at 3 to 5, 9 to 12 h at 6 and up, naps included. They say nothing about timing.
• Measured toddlers (34 months): nappers went to bed at 20:18 after a 103 minute nap, non-nappers at 19:35, both waking at 7:00. Melatonin rose at 19:10 to 19:48. Bedtimes close to or before melatonin onset meant long settling and resistance.
• Measured preschoolers (3 to 6, no nap): bed 20:01, wake 6:50, melatonin onset 19:26. Nappers at preschool: each hour of later nap end delayed sleep onset 16 minutes; each hour of nap cut the night by 14 minutes.
• Who still naps: nearly all 2-year-olds, about two thirds at 3, under half at 4, about 15% at 5, about 10% at 6.
• The consultant chart this started from ("The Complete 2 Year Old Sleep Chart") sits inside the guideline range but puts no-nap bedtimes 45 minutes earlier than measured toddlers and shifts bedtime a full minute per nap minute. For age 2 its value is shown above for comparison.

Every number in the model carries a tag: guideline, observed, consultant or assumption. Measured samples are small (14 to 85 children) and spreads are wide (35 to 75 minutes), so treat the result as a centre, not a rule.