HRV Calculator
Compute RMSSD and SDNN from your raw RR intervals, or check a known RMSSD against typical ranges for your age. The RR-interval mode is what most HRV calculators leave out.
How to use it
- Paste your RR/IBI intervals in milliseconds (exported from a chest strap or HRV app) to compute RMSSD, ln(RMSSD), and SDNN.
- Or switch to interpret mode and enter a known RMSSD plus your age.
- Compare your value against the typical resting range for your age band.
What is RMSSD and how is it calculated?
RMSSD is the root mean square of successive differences between consecutive RR intervals — the time gaps between heartbeats, in milliseconds. It is the most widely used short-term heart rate variability metric and primarily reflects parasympathetic (vagal) activity. Many apps report ln(RMSSD) to make day-to-day numbers easier to compare.
SDNN is the standard deviation of the RR intervals over the measurement window, capturing overall variability. A stable reading typically uses a consistent 1–5 minute window taken at the same time and posture each day.
What is a good HRV?
There is no universal 'good' number — HRV varies widely by age, genetics, and measurement method. Typical resting RMSSD tends to decline with age, from roughly 42–78 ms in the late teens and twenties to around 18–40 ms past 60. What matters most is your own baseline and trend, not where a single reading lands in a population band.
Frequently asked questions
How do I calculate HRV from RR intervals?
RMSSD is the square root of the mean of the squared differences between successive RR intervals. Paste your intervals in milliseconds and this calculator returns RMSSD, ln(RMSSD), and SDNN.
What is a normal RMSSD for my age?
Typical resting RMSSD declines with age — roughly 42–78 ms in your late teens and twenties, falling toward 18–40 ms past 60. These are population references for orientation; your personal baseline and trend are more meaningful.
Why does HRV drop after a hard workout?
Intense exercise shifts the autonomic nervous system toward sympathetic dominance and temporarily suppresses parasympathetic activity, lowering HRV. As you recover, HRV typically rebounds toward or above baseline.
Educational, performance-oriented content for athletes — not medical advice. Thresholds and reference ranges come from group data and vary between individuals.