Does the sleep calculator upload my data?

No. The core calculation runs in this browser. Permission-based device streams stay local unless you explicitly download a result.

How accurate is the result?

Accuracy depends on the inputs and hardware. The page labels estimates and calibration limits; use an approved instrument or official source for safety, medical, financial or travel decisions.

Can I use it offline?

Yes. The calculation and UI do not require an external API or account. Browser permissions and device sensors may still be unavailable on some platforms.

Sleep Cycle & REM Calculator — Free Online Tool

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Counting a Streak Correctly Means Using Local Dates, Not UTC Timestamps

Why a naive timestamp-based streak counter breaks near midnight in some timezones, and how counting backward from today through local calendar dates fixes it.