What is the Bedtime by Age Calculator?
This tool estimates the time your child should go to bed in order to wake up at a chosen time while still getting the amount of sleep recommended for their age. It works backwards from the wake-up time, subtracting the typical sleep need for the child's age group based on widely used pediatric sleep guidelines (such as those from the American Academy of Pediatrics and the CDC).
How to use it
Enter the child's age in years, then set the morning wake-up hour and minute (24-hour format, e.g. 7:00 for 7 AM). The calculator returns the recommended bedtime. Adjust the wake-up time to match a school start or daily routine and the bedtime will update accordingly.
The formula explained
The math is simple: Bedtime = Wake-up time − Recommended sleep hours. The recommended sleep figure depends on age — younger children need more sleep. We use the midpoint of each recommended range: toddlers (1–2) about 12.5 hours, preschoolers (3–5) about 11.5 hours, school-age children (6–12) about 10.5 hours, and teens (13–18) about 9 hours. Times wrap correctly across midnight.
$$\text{Bedtime} = \left( 60\,\text{Wake Hour} + \text{Wake Min} - 60\,S \bmod 1440 \right)$$
Worked example
A 7-year-old needs to wake at 7:00 AM. School-age children need about 10.5 hours of sleep. 7:00 minus 10 hours 30 minutes gives a bedtime of 20:30 — that is 8:30 PM.
$$\text{Bedtime} = \Big( 60\,\text{Wake Hour} + \text{Wake Min} - 60 \times 10.5 \Big) \bmod 1440$$
FAQ
Is this medical advice? No. It is a general guide using average sleep ranges. Individual needs vary; consult a pediatrician for sleep concerns.
Why does the bedtime sometimes show the previous evening? Sleep usually starts the night before, so a morning wake-up naturally maps to an evening bedtime.
Can I use it for adults? This tool is tuned for children and teens. Adults generally need 7–9 hours of sleep.
