Sleep Cycle Calculator
Find optimal bedtimes (or wake times) based on the 90-minute sleep cycle. Waking at the END of a full cycle feels rested; waking mid-cycle feels groggy. 3-6 cycles shown (4.5-9 hours). Recommended: 5-6 cycles (7.5-9 hours).
What powers the Sleep Cycle Calculator
Reverse-calculate bedtime from desired wake time
Forward-calculate wake time from bedtime
3-6 cycle options (4.5-9 hours)
Recommended cycles highlighted
Adjustable "time to fall asleep" buffer
Why the Sleep Cycle Calculator is different
Browser-native
The Sleep Cycle Calculator runs entirely in your browser. Input is processed locally — never uploaded, never logged, never cached anywhere outside your device.
No artificial limits
No daily quotas, no character ceilings, no "upgrade for more" walls. Every feature is the complete feature — the same on the first use as the thousandth.
Production-grade quality
Built to the same engineering bar as paid SaaS tools — accurate algorithms, audited logic, responsive design and accessibility-tested interactions.
Common use contexts
- Early morning flights / meetings — pick the right bedtime
- Avoiding groggy wake-ups
- Insomnia recovery
- Optimizing alarm time for work / school
Private and secure
Zero upload
All processing happens in your browser. Input is never transmitted, logged or cached.
Works offline
Once the page loads, the tool runs without an internet connection. No network calls happen during use.
No tracking
No accounts, no cookies for tool state. Only aggregate analytics count visits at the page level.