Why I Built This:
I couldn't find a sleep calculator that was:
- Fast on mobile
- Free without ads
- Actually explained the science
- Didn't require signup
So I built one from scratch in pure HTML/CSS/JS.
What is Sleep Calculator REM?
sleepcalculatorrem.com is a free tool that
calculates your optimal wake-up and bedtime
windows based on 90-minute REM sleep cycles.
Most people wake up groggy not because they
slept less — but because they woke up in the
MIDDLE of a sleep cycle.
This tool solves that.
Features
3 Calculation Modes
- Wake Up — enter bedtime → get best wake times
- Bedtime — enter wake time → get best bedtimes
- Sleep Now — calculates from current time instantly
Special Features
- 🧠 Visual REM cycle diagram
- 👶 Age-based sleep recommendations
- 📊 Sleep debt calculator (weekly tracker)
- ⚙️ Custom cycle length (85–110 min)
- ⏱️ Custom fall-asleep time setting
- 🌙 Dark mode by default
- 📋 One-tap copy alarm time button
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