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.
Calculator information
📋 How to use this calculator
- Enter your daily HRV reading in milliseconds (ms) from your wearable (RMSSD typically ranges 20-100 ms).
- Enter your age and sex for comparison against population baselines.
- For 7-day tracking, log HRV daily; the system computes your personal baseline and deviation.
- Add resting heart rate (RHR) and sleep duration for a composite Recovery Score.
- Click Calculate to see your HRV category (low/normal/high), interpretation, and today's training recommendation.
- 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:- Age 30-39 male range: mean RMSSD 35-48 ms (HRV 38 = low-normal)
- HRV_z = (38 - 45) / 8 = -0.875
- RHR_z = -(58 - 55) / 3 = -1.0 (negative = elevated RHR)
- Sleep score 70 -> normalized 0.7
- Recovery = 0.5 * (-0.875) + 0.3 * 0.7 + 0.2 * (-1.0) = -0.4375 + 0.21 - 0.2 = -0.43
- 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.
📚 Sources & references
Last updated: May 11, 2026