Eight Sleep HRV Explained: What Your Number Means

Your Eight Sleep HRV is a nightly average of readings taken continuously while you sleep — the mattress sensors sample your heart rhythm all night and roll it up into one number by morning. It's one of the best recovery signals your body produces, and sleep is the best time to measure it. Here's how to read it.

What HRV actually is

Heart rate variability is the variation in time between consecutive heartbeats, measured in milliseconds. A heart beating exactly once per second with zero variation has an HRV of 0 — and that's bad. Higher variability means your parasympathetic ("rest and digest") nervous system is in control: you're recovered, adaptable, ready for load. Lower-than-usual variability signals accumulated stress — training, illness, alcohol, poor sleep.

How Eight Sleep measures it

The Pod's sensor grid detects the tiny mechanical pulses of your heartbeat through the mattress all night, producing HRV readings roughly every five minutes (an RMSSD-based measure — the standard for sleep-time HRV). The number in the app each morning summarizes that whole night. This is a different approach from a watch, which is why the numbers rarely match — more on that below.

What's a "good" number?

Compare yourself only to yourself. The useful signal is your 7–30 day baseline and how tonight deviates from it: a dip of 15–20% below your own baseline after a hard workout, late meal, or a couple of drinks is meaningful; a friend's higher number is not.

Why it differs from your Apple Watch

• Different math: Apple Watch reports SDNN, Eight Sleep uses an RMSSD-based nightly measure. The two metrics scale differently — they're not supposed to match.
• Different timing: the Watch takes occasional spot readings, many during the day; Eight Sleep measures continuously during sleep, the gold-standard window.
• Different sensor: optical wrist sensor vs. mechanical bed sensing.

Both are internally consistent — trend each against itself, not against each other.

Tracking it in one place

Eight Sleep shows tonight's number, but never exports HRV to Apple Health, where recovery apps and long-term trends live. Nocturne bridges that: it exports your full overnight HRV series (or the nightly average — your choice) into Apple Health automatically each morning, and gives you 7/30/90-day HRV trend charts of its own. Setup guide: how to export Eight Sleep HRV.