Mentis- Adults generally need 7–9 hours. That's about five or six 90-minute cycles.
- Count back from your wake time and add about 15 minutes to fall asleep.
- Fix your wake time first, seven days a week. Bedtime follows.
How the sleep calculator works
Through the night you move through sleep cycles of light sleep, deep sleep and dream (REM) sleep. One cycle averages about 90 minutes. Waking at the end of a cycle, rather than in the middle of deep sleep, tends to feel less groggy. The calculator counts back four, five and six cycles from your wake-up time and adds 15 minutes, the time it typically takes to drift off.
It's a guide, not a law. Cycles vary from person to person and get shorter towards morning. If you wake groggy, move your bedtime 15 minutes earlier or later for a week and see.
How much sleep do you actually need?
An expert panel convened by the US National Sleep Foundation recommends 7–9 hours for adults aged 26–64, and 7–8 hours for over-65s (Hirshkowitz et al., 2015). Teenagers need 8–10. You'll know you're in your range when you wake without much of a fight and don't crash mid-afternoon.
The habit that matters more than bedtime
Most people try to fix their sleep by going to bed earlier. Sleep specialists start from the other end: a fixed wake-up time, every day, weekends included. It's the anchor of cognitive behavioural therapy for insomnia (CBT-I), the approach with the strongest evidence for long-term better sleep. In a meta-analysis of CBT-I trials, people fell asleep about 19 minutes faster and spent about 26 fewer minutes awake during the night (Trauer et al., 2015).
Regularity matters beyond sleep itself. In a study of more than 60,000 people wearing activity trackers, how regular their sleep was predicted their risk of dying early even better than how long they slept (Windred et al., 2024). And sleeping in late at weekends shifts your body clock like a mini jet lag every Monday, which researchers call "social jetlag" (Wittmann et al., 2006).
Tips to fall asleep at your new bedtime
- Let light in within an hour of waking. Morning light sets your clock for the night ahead.
- Cut caffeine by early afternoon. That 5pm chai is still in your system at 11.
- Give the last hour a shape: phone face down, lights low, something dull and calm.
- Only go to bed when sleepy. If you're awake after about 20 minutes, get up, sit somewhere dim, and come back when you're drowsy.
- Breathe it out with the 4-7-8 breathing timer.
Building the habit with the Mentis Sleep plan
The Mentis Sleep plan turns these ideas into small daily steps over nine chapters: "The first honest look", "A time I wake up", "The hour before bed", "Nothing borrowed" (caffeine and alcohol), "Bed means sleep", "No more weekend debt" and "The 3am mind". Activities like "Let The Light In Before The Alarm", "Set The Weekend Alarm" and "Try A Warm Shower Before Bed" each take a few minutes. A short check-in each morning lets Mimi spot what's moving your sleep. See our full guide to better sleep.
Frequently asked questions
What time should I sleep if I wake up at 6am?
For about 7.5 hours of sleep (five cycles), be in bed with the lights off around 10:15pm. For 9 hours, around 8:45pm. For 6 hours, around 11:45pm.
Are sleep cycles always 90 minutes?
No. A cycle averages about 90 minutes but varies from roughly 70 to 120 minutes between people and through the night. Treat the calculator as a rough guide and adjust by 15 minutes based on how you feel.
How many hours of sleep do adults need?
Most adults do best on 7 to 9 hours, according to the US National Sleep Foundation's expert panel. Some people need a little less or a little more.
Is it better to fix my bedtime or my wake time?
Your wake time. Getting up at the same time every day anchors your body clock, and your bedtime follows. Sleep researchers have found that regular sleep timing predicts health even more strongly than sleep length.
Can I catch up on sleep at the weekend?
Sleeping in a little is fine, but a big gap between weekday and weekend wake times shifts your body clock, a bit like flying to a different time zone and back every week. Keep the gap within an hour.
- Hirshkowitz M et al. (2015). National Sleep Foundation's sleep time duration recommendations. Sleep Health 1(1):40–43.
- Windred DP et al. (2024). Sleep regularity is a stronger predictor of mortality risk than sleep duration. Sleep 47(1):zsad253.
- Trauer JM et al. (2015). Cognitive behavioral therapy for chronic insomnia: a systematic review and meta-analysis. Annals of Internal Medicine 163(3):191–204.
- Wittmann M, Dinich J, Merrow M, Roenneberg T. (2006). Social jetlag: misalignment of biological and social time. Chronobiology International 23(1–2):497–509.