Heart Rate Variability Calculator

Calculate Standard Deviation of R-R Intervals (SDNN), a key measure of Heart Rate Variability to assess autonomic nervous system function.

Input Parameters

Example format: 800 810 795 805 790

Auto-filled from data, but can be adjusted if needed

Calculation Results

Standard Deviation of R-R Intervals (SDNN)

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SDNN is calculated as the standard deviation of all R-R intervals in milliseconds.

Interpretation:

  • High SDNN (>75 ms): Good autonomic function
  • SDNN 50-75 ms: Fair autonomic function
  • SDNN <50 ms: Poor autonomic function

Calculation Formula

SDNN = σ(R-R intervals)

Where:
σ = standard deviation
R-R intervals = time intervals between consecutive heartbeats

Heart Rate Variability Calculator Usage Guide

Learn how to use the Heart Rate Variability Calculator and understand the results

How to Use This Calculator

  1. Enter your R-R intervals in milliseconds. Each R-R interval is the time between consecutive heartbeats measured in milliseconds. You can enter them one per line or separated by spaces.
  2. The calculator will automatically count the number of intervals you've entered.
  3. Click the "Calculate" button to compute the Standard Deviation of R-R Intervals (SDNN).
  4. The result will be displayed in milliseconds, with an interpretation guide.

Understanding Heart Rate Variability (HRV)

Heart Rate Variability (HRV) is the variation in time between consecutive heartbeats. It reflects the activity of the autonomic nervous system, which controls involuntary bodily functions. HRV is an important indicator of overall health and well-being.

What is SDNN?

SDNN is one of the simplest and most widely used HRV metrics. It measures the overall variation in heart rate by calculating the standard deviation of all R-R intervals in a short-term ECG recording (typically 24 hours). A higher SDNN generally indicates better autonomic nervous system function.

How to Collect R-R Intervals

You can collect R-R intervals using:

  • Heart rate monitors with R-R interval measurement capabilities
  • Wearable fitness trackers (like Apple Watch, Garmin, Fitbit) that provide HRV measurements
  • ECG (Electrocardiogram) machines

Interpreting Your Results

The SDNN value provides insights into your autonomic nervous system balance:

  • SDNN > 75 ms: Excellent autonomic function (parasympathetic dominance)
  • SDNN 50-75 ms: Fair autonomic function (balanced autonomic activity)
  • SDNN < 50 ms: Poor autonomic function (sympathetic dominance)

Keep in mind that HRV varies throughout the day and is influenced by factors like sleep quality, stress levels, exercise, and hydration. For accurate assessment, it's recommended to track HRV over several days.