Schlafrechner

Most adults need 4 to 6 complete sleep cycles per night. Five cycles (7.5 hours) is the sweet spot for most people, providing enough deep and REM sleep without leaving you groggy. Four cycles can work if your schedule demands it; six is ideal for recovery days.

Adults aged 18–64 generally need 7–9 hours per night. Teenagers need 8–10 hours and older adults typically do well with 7–8 hours. Consistently sleeping fewer than 6 hours is linked to impaired cognition, metabolism issues, and increased disease risk.

The best bedtime is the one that lets you wake naturally after completing full 90-minute cycles. For most working adults, sleeping between 10 pm and midnight aligns well with natural circadian rhythms and melatonin release patterns.

Each 90-minute cycle moves through light sleep, deep (slow-wave) sleep, and REM sleep. Waking at the end of a cycle — rather than mid-deep-sleep — means you surface naturally and feel alert. The 90-minute figure is an average; individual cycles range from roughly 80 to 110 minutes.