How to make sense of the HRV number on your Fitbit
Engadget explains that Fitbit's HRV reading has no score to beat, and that your own trend over time says more than any comparison with other people.
The facts
- According to Engadget, HRV measures the time difference between heartbeats and is shown in milliseconds, not beats per minute.
- Google calculates it using a method called RMSSD, based on the longest sleep period in the previous 24 hours, and only sleep lasting more than three hours qualifies.
- Google does not set a universally good HRV reading, because age, fitness and individual physiology all play a part. Your personal range is based on up to 30 days of data.
- Engadget cites a 2024 study on the Fitbit Charge 4 that found moderate to strong agreement with reference measurements, with a tendency to underestimate HRV.
Case notes · Danny's take
Why it matters
A number on your wrist feels like a verdict. It isn't one. Fitbit's HRV only means something against your own baseline, so a friend's 80 ms tells you nothing about your 24 ms. Same lesson as in markets: a figure without context is noise, and the trend is the evidence.
For builders
Different brands use different HRV calculations, RMSSD on Fitbit and SDNN on Apple's Watch, so cross-brand comparisons mislead users. If you build health or wellness apps on wearable data, show personal trends and ranges, not one headline number.
Not financial advice. Do your own investigation.
This story was summarised with AI from Engadget's reporting and checked against our editorial policy. Danny's take reflects his views. Disclaimer.
Danny Walter
Founder of Moon Republic, Volt Terminal and Moon Republic Academy. Author of The Market Is a Crime Scene and After the Applause.