Wake up feeling rested. This free sleep calculator uses 90-minute sleep cycles to suggest the best times to go to bed or wake up – so you finish a cycle instead of being jolted out mid-sleep.
Based on ~90-minute sleep cycles. Waking at the end of a cycle can feel easier than mid-cycle. Cycle length varies by person – use these as a guide.
How Sleep Calculator Works
This tool works backward or forward from a target time using 90-minute sleep cycles, so you get a short list of times that line up with the end of a full cycle instead of the middle of one. You can plan from a wake-up time or from a bedtime.
Formula: One sleep cycle = 90 minutes. If working from a wake-up time: bedtime = wake time − time to fall asleep − (cycles × 90 minutes). If working from a bedtime: wake time = bedtime + time to fall asleep + (cycles × 90 minutes). The calculator shows results for 6, 5, 4 and 3 full cycles.
- Mode — whether you’re entering a wake-up time or a bedtime
- Time — your target wake-up time or bedtime
- Time to fall asleep — minutes you typically take to fall asleep (defaults to 15)
Example Scenarios
| Mode | Target time | Cycles | Suggested time |
|---|---|---|---|
| Wake up at | 7:00 AM | 6 | Bedtime: 9:45 PM |
| Wake up at | 7:00 AM | 5 | Bedtime: 11:15 PM |
| Wake up at | 7:00 AM | 4 | Bedtime: 12:45 AM |
| Go to bed at | 11:00 PM | 6 | Wake time: 8:15 AM |
| Go to bed at | 11:00 PM | 5 | Wake time: 6:45 AM |
| Go to bed at | 11:00 PM | 4 | Wake time: 5:15 AM |
Sleep Calculator FAQ
Why does the calculator suggest multiple bedtimes instead of just one?
Because it counts back in full 90-minute cycles, there isn’t one “correct” bedtime — there’s a set of times, each corresponding to a different number of complete cycles (6, 5, 4, or 3). More cycles generally means more total sleep.What is a sleep cycle and why is 90 minutes used?
A sleep cycle is one pass through the stages of light sleep, deep sleep, and REM sleep. Ninety minutes is a commonly used average cycle length, which is why the calculator uses it as its base unit for the suggested times.How does “time to fall asleep” affect the results?
The calculator adds this buffer on top of your sleep cycles when working from a wake-up time, or before them when working from a bedtime, so the suggested time reflects when you actually need to lie down, not just when sleep starts.Is it better to wake up at the end of a sleep cycle?
Many people report feeling less groggy waking at the end of a cycle, when sleep is lighter, compared to being woken mid-cycle during deep sleep. This calculator is built around that idea, though individual experience varies.Does everyone’s sleep cycle actually last exactly 90 minutes?
No — actual cycle length varies from person to person and even night to night, roughly in the 80-120 minute range. The 90-minute figure used here is a widely cited average, so treat the results as a starting guide.How many sleep cycles should I aim for in a night?
Five to six cycles (roughly 7.5 to 9 hours) is a commonly referenced target range for adults, which is why those options appear first in the results. Your own ideal amount can differ based on age and lifestyle.Related Calculators
If you’re consistently short on rest, the sleep debt calculator can help track how much you’ve lost over time, while the caffeine half-life calculator shows how late-day caffeine might be affecting your bedtime. If screens before bed are a factor, the screen time calculator is worth a look too.