Sleep Calculator
Find the perfect time to go to bed or wake up based on natural 90-minute sleep cycles to avoid grogginess and maximise rest.
Calculate Your Optimal Sleep Times
Choose whether you want to set your wake-up time or your bedtime, and we will calculate the best times based on 90-minute sleep cycles.
Sleep Cycle Estimator
Factor in sleep latency to wake up at the end of a natural cycle.
How it Works
The science of sleep cycles
The 90-Minute Rule
Human sleep occurs in cycles of approximately 90 minutes, progressing through light, deep, and REM sleep stages.
Avoid Sleep Inertia
Waking up in the middle of deep sleep causes grogginess. Waking at the end of a cycle leaves you feeling refreshed.
Sleep Latency
It takes the average person 15 minutes to fall asleep. We add this buffer so your cycles align perfectly with your alarm.
Optimal Duration
Most adults function best on 5 cycles (7.5 hours) or 6 cycles (9 hours) of sleep per night.
Understanding Sleep Stages
A quick reference table for the different stages of sleep you experience during a single 90-minute cycle.
| Stage | Name | Duration | Purpose |
|---|---|---|---|
| N1 | Light Sleep | 1–5 mins | Transition between wakefulness and sleep. Muscle tone relaxes. |
| N2 | Deeper Light Sleep | 10–25 mins | Heart rate slows, body temperature drops. Prepares for deep sleep. |
| N3 | Deep Sleep (SWS) | 20–40 mins | Physical restoration, tissue repair, and immune system strengthening. |
| REM | Rapid Eye Movement | 10–60 mins | Memory consolidation, learning, and emotional processing. Dreaming occurs. |
Sleep Calculator FAQ
Answers to the most frequently asked questions about sleep cycles, sleep inertia, and healthy sleep habits.
A sleep cycle is a recurring pattern of sleep stages that lasts approximately 90 minutes. It includes light sleep, deep sleep, and REM (Rapid Eye Movement) sleep. Waking up at the end of a cycle, rather than in the middle of deep sleep, helps you feel more refreshed.
This feeling is called ‘sleep inertia’. It occurs when you wake up during the deep sleep stage of a cycle. By timing your wake-up to coincide with the end of a 90-minute cycle, you can significantly reduce or eliminate this grogginess.
On average, it takes a healthy adult about 15 to 20 minutes to fall asleep. This is known as ‘sleep latency’. The calculator factors in a default 15-minute buffer to ensure your sleep cycles align perfectly with your alarm.
Most adults need between 4 to 6 sleep cycles per night, which equates to 6 to 9 hours of sleep. Five cycles (7.5 hours) is generally considered the optimal target for feeling fully rested and alert during the day.