RMSSD.COM — HRV REFERENCE
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RMSSD Calculator for RR Intervals

Paste a sequence of RR or normal-to-normal intervals in milliseconds to calculate the root mean square of successive differences. Review the input and exclusions before interpreting the result. RMSSD is an HRV measure, not a diagnosis or a complete assessment of stress, recovery or heart health.

Enter Your Interval Data

Accepted input should include one interval per line or values separated by commas, spaces or tabs. Use milliseconds unless the unit control is explicitly changed. Remove timestamps, heart-rate values and text labels before calculation.

Example input: 1010, 985, 1002, 1030, 1018

Parsed values: 5

Calculations occur locally in your browser.

Start a Live HRV Session

How RMSSD Is Calculated

The calculator finds the difference between each accepted interval and the interval immediately before it. It squares those differences, calculates their arithmetic mean and takes the square root.

RMSSD = square root of the mean of each squared successive RR difference

For the example above, the successive differences are −25, 17, 28 and −12 milliseconds. Their squares are 625, 289, 784 and 144. The mean squared difference is 460.5, and its square root is approximately 21.46 milliseconds.

Review Data Quality First

One mistyped, missed or extra beat can change RMSSD substantially. The calculator should flag impossible or improbable entries but should not silently rewrite a dataset. Automatic thresholds cannot tell whether an unusual interval is an artifact, an ectopic beat or a real rhythm change.

How to Read the Result

RMSSD describes short-term variation between consecutive accepted intervals. It is influenced by respiration and is commonly used as an index of vagally mediated HRV, but it should not be reduced to a universal good or bad category. Age, measurement duration, posture, breathing, time of day, activity, illness, medication, device and processing method can all affect the value.

For personal tracking, compare measurements collected with the same protocol and look for patterns across several sessions. For research, document sensor type, sampling or transmission method, recording length, artifact handling and the exact formula.

To collect a consistent live recording, follow How to Measure HRV Consistently. To inspect the shape of consecutive intervals, use the Poincaré plot guide.

Privacy

The input area should state whether calculations occur locally in the browser. If data are uploaded, logged or stored, obtain informed consent and explain retention and deletion. Users should remove names, dates of birth, record numbers and other identifiers before pasting research or clinical data.

Frequently Asked Questions

What data do I enter into an RMSSD calculator?
Enter successive RR or normal-to-normal intervals, usually in milliseconds. Do not enter beats per minute unless the tool explicitly converts heart rate to intervals and explains the limitations.
How many RR intervals do I need?
The result needs at least two intervals, but a tiny sample is unstable and unsuitable for meaningful interpretation. A consistent five-minute resting recording is a common short-term format.
Are RR and NN intervals the same?
RR describes detected intervals between R waves or beats. NN refers to intervals accepted as normal-to-normal after review. The distinction matters when artifacts or non-sinus beats are present.
What is lnRMSSD?
lnRMSSD is the natural logarithm of RMSSD. It is often used in analysis because RMSSD distributions can be skewed. The tool should show it only when RMSSD is greater than zero and label the transformation.
What is a normal RMSSD?
There is no single normal value for every person and protocol. Interpret a value in the context of the individual, measurement conditions and an appropriate reference dataset.
Can RMSSD detect an arrhythmia?
No. Irregular rhythms can alter RMSSD, but the metric cannot identify the cause. Concerning symptoms or rhythm questions require appropriate medical evaluation.