HRV baseline is your personal reference line for heart-rate variability, usually calculated as a 7- to 14-day rolling average of overnight RMSSD. It is the anchor against which daily readings are read as "higher than mine" or "lower than mine" — absolute HRV numbers are close to useless across individuals.
Why it matters
HRV responds to autonomic nervous system balance, so it drifts with training load, sleep debt, alcohol, illness, and supplement-driven stimulation. A single day's HRV means almost nothing; the distance from your own baseline means a lot. This is the metric most podcast hosts and performance coaches cite, and it is the most useful non-blood signal most users have.
How the baseline is built
Most wearables (Oura, Whoop, Garmin, Apple Watch) compute overnight HRV during sleep, then smooth it with a rolling window:
- 7-day average — reactive, picks up training or sleep shocks quickly
- 14-day average — the standard for most readiness scoring
- 28-day average — slower but useful for confirming a real trajectory change
Unfair reads whichever window your device exposes and stores the daily value alongside dose events through HealthKit integration. It then compares each day against your moving average window rather than population norms.
Interpreting a shift
A sustained HRV increase of roughly 5–10 ms above your baseline over several weeks is the signal most athletes chase from recovery protocols. A sustained drop of similar magnitude is worth investigating before stacking anything stimulatory. Since HRV is one of the most trusted biomarkers for supplement evaluation, it features in recommendation ranking when wearable data is available.
Known caveats
- HRV is highly sensitive to measurement conditions — strap vs. ring vs. wrist readings are not interchangeable.
- Alcohol, late meals, and high caffeine after noon all suppress HRV for 24–48 hours; confounders can easily be mistaken for supplement effects.
- Chronic stress can compress the range of normal variation, flattening the signal.
How this appears in Unfair
HRV baseline powers one of the default objective proxy slots for recovery and sleep-focused stacks. Daily values are plotted against the rolling baseline on the outcomes chart so delta changes are legible at a glance.
Clinical safety note
A sudden and sustained HRV collapse (more than ~15% below baseline for a week) in the absence of obvious lifestyle cause is worth discussing with a clinician, particularly if combined with elevated resting heart rate or new cardiac symptoms.