Sleep Cycle By Age is a free online sleep calculator that helps users plan their bedtime or wake time based on 90 minute sleep cycles and age specific sleep recommendations. The tool is designed to align waking moments with the end of a complete sleep cycle, which can reduce grogginess and make mornings easier. It is intended as a general guide and does not constitute medical advice; users with specific sleep issues or infants should consult a professional. The calculator offers a straightforward interface. Users enter their age and either the time they plan to go to bed or the time they need to wake up. The tool then maps the input against typical 90 minute sleep cycles and age based sleep hour guidelines, returning several suggested times that correspond to the end of a full cycle. Additional features include a list of recommended sleep hours by age, suggested bedtimes, and guidelines for improving sleep hygiene, such as maintaining a consistent schedule, optimizing the sleep environment, limiting screen time before bed, and avoiding caffeine after midday. Typical use cases include planning bedtime for a fixed wake schedule, such as work or school, or choosing a wake time when the schedule is flexible. The tool works across all age ranges, from toddlers to older adults, and users are encouraged to treat the results as a starting point, adjusting by small increments based on personal experience. Revisiting the calculator after routine changes, such as a new job or travel, is recommended. Technically, the calculator relies on the standard 90 minute sleep cycle model and incorporates age based sleep hour recommendations from established guidelines. No account or installation is required; the tool operates entirely through a web browser at sleepcyclebyage.com. The process takes less than a minute, and results are displayed immediately.