What this calculator does
The Recommended Sleep Hours by Age Calculator tells you how much sleep is appropriate for your age group and works out the bedtime you should aim for based on when you need to wake up. It uses the widely cited National Sleep Foundation age bands, which set different sleep needs for newborns, children, teenagers, adults and older adults.
How to use it
Enter your age in years, then enter the hour and minute you need to wake up (using a 24-hour clock, so 7:00 AM is hour 7, minute 0). The calculator finds your recommended sleep range, takes the midpoint, and subtracts it from your wake time to suggest a target bedtime. It also shows the earliest and latest bedtimes that still keep you inside the healthy range.
The formula explained
First, the recommended sleep band is selected from your age: newborns 14-17h, infants 12-16h, toddlers 11-14h, preschoolers 10-13h, school-age 9-12h, teens 8-10h, adults 7-9h, and 65+ 7-8h. Bedtime is then simply Wake Time − Recommended Hours. If the result falls before midnight, it correctly wraps to the previous day.
$$\text{Bedtime} = \left( \text{Wake Hour} \times 60 + \text{Wake Minute} - \text{Mid} \times 60 \right) \bmod 1440$$
$$\begin{gathered} \text{Bedtime}_{\text{min}} = \Big( W - \text{Mid}\times 60 \Big) \bmod 1440 \\[1.5em] \text{where}\quad \left\{ \begin{aligned} W &= \text{Wake Hour} \times 60 + \text{Wake Minute} \\ \text{Mid} &= \frac{\text{Low} + \text{High}}{2}\ \text{(hrs, by } \text{Age}\text{)} \end{aligned} \right. \end{gathered}$$
Worked example
A 30-year-old needs 7-9 hours, with a midpoint of 8 hours. If they wake at 07:00, bedtime is \( 07{:}00 - 8{:}00 = 23{:}00 \) (11:00 PM). To get the maximum 9 hours they would sleep at 22:00, and for the minimum 7 hours, 00:00.
FAQ
Are these medical recommendations? They are general guidelines from sleep research, not personalized medical advice. Individual needs vary.
Why a range instead of one number? Sleep needs differ between people of the same age, so health bodies publish a healthy range rather than a single value.
What if I wake very early? The calculator handles bedtimes that fall on the previous calendar day automatically.
