There is no universal 'good' HRV number. The same RMSSD can be below average for a 25-year-old and excellent for a 60-year-old, and every wearable reports it a little differently. This guide explains how to read your HRV against age- and sex-matched norms, why the trend beats the absolute value, and what actually moves the needle.

Why HRV has to be scored by age and sex

Heart rate variability falls steadily with age as the autonomic nervous system stiffens — overnight RMSSD averages roughly 60 ms in the 20s, around 45 ms in the late 30s, near 30 ms in the late 50s, and about 24 ms by 70. A reading of 40 ms is unremarkable at 30 but above average at 60. Sex differences are small but real, so this tool matches you to an age- and sex-specific band drawn from large population and wearable datasets, then reports where you land as a percentile.

Why your device changes the number

Absolute HRV depends heavily on how and when it is measured. A chest strap or clinical ECG taken at rest reads lower than an overnight wearable average; WHOOP samples during deep sleep and tends to read high; Apple Watch takes sporadic daytime SDNN samples that run noisier and lower. Because of this, comparing your WHOOP number to a friend's Oura number is meaningless. This calculator is calibrated to overnight wearable readings and foregrounds the caveat that you should compare against your own baseline on your own device.

The trend matters more than any single reading

One night's HRV swings with sleep, alcohol, late meals, travel, stress, and the first hours of an illness. That is why a personal baseline — a rolling 30–60 day average — is the reference that matters. A reading more than about 10% below your baseline is 'suppressed' and is a cue to recover; a stable or rising trend over weeks is the real signal of improving fitness and resilience. Chasing a single low morning is how people misread HRV.

What actually raises HRV

The levers with the strongest evidence are consistent, sufficient sleep; a regular aerobic base built without chronic overtraining; cutting evening alcohol; slow (~6 breaths per minute) breathing; and finishing meals earlier. None of these move a single night dramatically, but together they lift your baseline over weeks. If your HRV is persistently low for your age, or drops sharply without an obvious cause, treat it as a prompt to talk to a clinician — not as a diagnosis from this tool.