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HRV (Heart Rate Variability) Calculator

Interpret HRV score (RMSSD), 7-day tracking, recovery score combining sleep & RHR, and evidence-based tips to improve HRV.

HEALTH

HRV (Heart Rate Variability) calculator to interpret data from wearables such as WHOOP, Oura Ring, and Apple Watch — a key indicator of recovery and cardiac fitness.

Four tabs: HRV category by age (RMSSD), 7-day tracking with baseline, combined recovery score (HRV + sleep + RHR), and evidence-based tips to raise HRV (meditation, breathwork, sleep hygiene).

Disclaimer: HRV varies between individuals. Consult a doctor if you see a sustained drop or have cardiac symptoms.

HRV Calculator (Heart Rate Variability)

Analyze HRV from your wearable (Oura, WHOOP, Apple Watch, Garmin). Check category, daily trend, recovery score, and tips to improve HRV. Estimates only - not a medical diagnosis.

HRV Category by Age

Enter your RMSSD (ms) from your wearable. Norms differ by age and gender.

Estimates for lifestyle tracking only. Abnormal HRV, very high/low RHR, or other medical symptoms require physician consultation.

Calculator information

How to use this calculator

  1. Enter your daily HRV reading in milliseconds (ms) from your wearable (RMSSD typically ranges 20-100 ms).
  2. Enter your age and sex for comparison against population baselines.
  3. For 7-day tracking, log HRV daily; the system computes your personal baseline and deviation.
  4. Add resting heart rate (RHR) and sleep duration for a composite Recovery Score.
  5. Click Calculate to see your HRV category (low/normal/high), interpretation, and today's training recommendation.
  6. Open the Tips tab for evidence-based interventions to boost HRV (meditation, breathwork, sleep hygiene).

RMSSD and Recovery Score (Polar/Whoop methodology)

RMSSD = sqrt(sum((RR_i+1 - RR_i)^2) / (n-1)); Recovery Score = 0.5 * HRV_z + 0.3 * Sleep_quality + 0.2 * RHR_z
  • RR = successive R-R intervals from ECG (ms)
  • n = number of intervals in the measurement window (typically 5 minutes)
  • HRV_z = z-score of HRV vs. personal 30-day baseline
  • Sleep_quality = score 0-100 (duration + efficiency)
  • RHR_z = inverted z-score of resting heart rate (lower RHR = better)

HRV varies 20-30% day to day. Compare against your personal baseline, not others. Measurements are most reliable first thing in the morning (morning readiness).

Worked example: 35-year-old male, daily HRV = 38 ms, 30-day baseline = 45 ms

Given:
  • Age: 35, male
  • Today's HRV (RMSSD): 38 ms
  • 30-day baseline: 45 ms (SD +/-8)
  • Resting HR: 58 bpm (baseline 55, SD 3)
  • Last night's sleep: 6.5 hours (score 70/100)
Steps:
  1. Age 30-39 male range: mean RMSSD 35-48 ms (HRV 38 = low-normal)
  2. HRV_z = (38 - 45) / 8 = -0.875
  3. RHR_z = -(58 - 55) / 3 = -1.0 (negative = elevated RHR)
  4. Sleep score 70 -> normalized 0.7
  5. Recovery = 0.5 * (-0.875) + 0.3 * 0.7 + 0.2 * (-1.0) = -0.4375 + 0.21 - 0.2 = -0.43
  6. Scaled 0-100: 50 + (-0.43 * 15) ~ 43/100

Result: Recovery score 43/100 (Yellow/Recovery needed). Recommendation: low-intensity Zone 2 or active recovery; aim for 7-8 hours of sleep tonight.

Frequently asked questions

What is HRV and why does it matter?
Heart Rate Variability is the variation in time between successive heartbeats. High HRV signals a balanced autonomic nervous system (parasympathetic dominance at rest), while low HRV indicates stress, illness, or overtraining. HRV predicts cardiovascular mortality and aerobic fitness. A 1-5 minute morning measurement gives a useful readiness score.
What is a normal HRV for my age?
Average RMSSD by age: 20-29 = 50-70 ms, 30-39 = 35-55 ms, 40-49 = 30-45 ms, 50-59 = 25-40 ms, 60+ = 20-35 ms. Men typically run 10-15% lower than women at younger ages, with parity above 50. Endurance athletes can reach 80-150 ms. The absolute number matters less than your personal trend.
How do I improve HRV?
Evidence-based interventions: (1) sleep 7-9 hours consistently, (2) Zone 2 aerobic training (60-70% MHR) 150 minutes/week, (3) 10 minutes/day of meditation or breathwork (slow breathing at 6 breaths/min raises HRV ~20%), (4) limit alcohol (each drink can drop HRV ~30%), (5) cold exposure 2-3 minutes after workouts, (6) eat omega-3-rich foods.
Are wearable HRV readings accurate?
Optical (PPG) wearables like Apple Watch, Garmin, and Whoop achieve 85-95% accuracy vs. clinical ECG (the gold standard) for resting measurements. Accuracy drops during exercise due to motion artifacts. Chest straps like the Polar H10 are most accurate (>98%). Continuous overnight measurement is more reliable than daytime spot checks.
Is low HRV always bad?
Not always. Short-term dips are normal after hard training, high stress, or poor sleep - the body is prioritizing recovery. Persistently low HRV (below baseline for more than 7 days) can signal overtraining, subclinical illness, or burnout. HRV also declines naturally with age and during fever. See a clinician if RHR stays elevated >5 bpm while HRV drops.

Last updated: May 11, 2026

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