Sleep Time Calculator
Calculate the best bedtime or wake-up time based on the 90-minute sleep cycle.
Free tool — no app or signup needed.
Recommended Times
* Calculations include your selected fall-asleep time.
About
Human sleep alternates between REM (light) and non-REM (deep) sleep in cycles of approximately 90 minutes. Waking up at the end of a complete cycle helps you feel refreshed and alert.
This tool adds the average time it takes to fall asleep (about 15 minutes) and calculates your ideal bedtime or wake-up time automatically.
How to Use
- Sleep Now: Calculates the best wake-up times if you fall asleep right now.
- Set Wake Time: Works backward from your alarm time to suggest when to sleep.
- Power Nap: Finds the perfect length for a nap to boost your daytime performance without grogginess.
- Winding Down: Creates a custom evening routine schedule (cutting off caffeine, screen time, etc.) leading up to your chosen bedtime.
Glossary
- REM Sleep (Rapid Eye Movement)
- The phase of sleep characterized by active brain waves and dreaming. Because your brain is active, waking up during a REM phase makes you feel incredibly refreshed and alert.
- Non-REM Sleep / Deep Sleep
- The restorative phase of sleep where the body repairs tissue and boosts immune function. Being abruptly awakened during Deep Sleep causes severe grogginess.
- Power Nap
- A short sleep taken during the day. Keeping it to around 20 minutes (micro-nap) ensures you wake up before entering deep sleep, highly boosting your performance.
- The 90-Minute Rule
- A complete sleep cycle (Non-REM + REM) averages about 90 minutes. Our calculator perfectly orchestrates your wake-up times to align exactly with the end of these 90-minute boundaries.
- Circadian Rhythm
- Your body’s internal 24-hour biological clock regulating sleep-wake cycles. Irregular bedtimes severely disrupt this mechanism, crushing your sleep quality.
FAQ
- Q.Why is the math always based on 90-minute jumps?
- Clinical studies show sleep operates in wave cycles of deep and light sleep roughly every 90 minutes. Awakening precisely at the end of a light wave completely circumvents morning fatigue.
- Q.Is the 90-minute cycle definitively exact for everyone?
- No, 90 minutes is the global adult median. A cycle might organically be 80 or 100 minutes depending on your genetics or exhaustion. Use 90 as the baseline and adjust manually based on feeling.
- Q.How long should a power nap be using this logic?
- For a power nap, you absolutely do not want to enter the deep sleep cycle. Use our "Power Nap" tab to easily figure out the best micro-nap (20 mins) or full-cycle nap (90 mins).
- Q.Why cut off blue light before bed?
- Light from screens suppresses melatonin, the sleep hormone. The winding-down schedule helps you remember to put screens away 1 hour before sleeping.
Use Cases
Efficient Waking
Calculate backward from your alarm time to find the exact moment to sleep so you wake up refreshed at the end of a cycle.
Power Nap Productivity
Take a quick 20-minute power nap in the afternoon to restore concentration and brain fatigue without grogginess.
Repay Sleep Debt
Take a perfect 90-minute full cycle nap on your off days to recover without destroying your night sleep schedule.
Improve Sleep Onset
Use the winding down schedule feature to step away from screens and create the perfect sleep environment.
Send Feedback
Please let us know your thoughts to help us improve the tool.
Feedback is temporarily suspended
The server is busy or spam protection is active. Please try again later.