How to read it: Each colored line is the mean total sleep at each age (from published tables). The shaded bands cover the middle 50% of children at each age (the interquartile range, P25 to P75). At any given age, half of the children in the sample sleep within the band; a quarter sleep less than the band's bottom edge, and a quarter sleep more than the top edge. The band gets narrower as children get older, individual variation in sleep duration is much larger in infancy than in school age. The guidelines most parents encounter (e.g., NSF, AAP) group children into wide age ranges (e.g., "6 to 13 years"). These lines show year-by-year parent-reported sleep at each age, so a parent can see what families actually report rather than estimating from a multi-year average. These are descriptive data. They show what parents report is happening with their children's sleep. They do not represent recommendations for how much your child should sleep.

Note on variability bands and methodology: Each shaded band shows the interquartile range (IQR, P25 to P75), which covers the middle 50% of children at each age. Switzerland and Germany both publish percentile data directly, from which P25 and P75 can be extracted (Iglowstein 2003 Figure 1 uses Gaussian-fitted percentiles from mean and SD; Schlarb 2015 Figure 2 uses empirical 4th-order polynomial-smoothed percentiles). For the United States and China, the source papers published mean and SD per age; P25 and P75 were computed assuming normality (the same Gaussian approach Iglowstein used for Switzerland). Nap handling verified paper-by-paper: Iglowstein 2003 Table 1 reports separate Nighttime and Daytime Sleep columns summed to a Total Sleep column (we use Total). Schlarb 2015 / KiGGS asks parents "how many hours does your child sleep per day and night averagely" and the paper explicitly labels the outcome "total amount of sleep per day." Cespedes 2014 Project Viva asks parents to report total sleep duration at ages 6 months through 7 years (explicitly including morning naps, afternoon naps, and nighttime sleep at younger ages). Li 2013 asks CSHQ "daily total sleep duration during a typical week" which at ages 5+ is dominantly nighttime sleep because Chinese primary school children rarely nap. All four lines are therefore approximately 24-hour total sleep at the ages shown. Sample details: Cespedes et al. 2014 is a longitudinal birth cohort from eastern Massachusetts (Project Viva), not a US national sample. Li 2013 is a school-age cohort from 8 Chinese cities, parent-administered CSHQ; preschool ages are not covered by this single-source line. No single published paper provides multi-age-range Chinese parent-report data with per-year SDs. On single-source lines: every country line is drawn from one cohort with one instrument, by deliberate methodological choice. When ages differ (USA ends at 7, China starts at 5), that reflects what the literature actually supports rather than a composite stitched across populations. Williams 2013, Meltzer 2021, Barreira 2022, Mindell 2010/2013, Liu 2005, and Wu 2018 were all considered and rejected as single-source lines for their respective countries.