I Built a Free Sleep Calculator in Pure HTML/CSS/JS — No Frameworks, No Libraries, 98 Desktop Speed
Published: (June 13, 2026 at 03:02 AM EDT)
1 min read
Source: Dev.to
Source: Dev.to
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. sleepcalculatorrem.com is a free tool that Most people wake up groggy not because they This tool solves that. Wake Up — enter bedtime → get best wake times Bedtime — enter wake time → get best bedtimes Sleep Now — calculates from current time instantly 🧠 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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