What Is a Good HRV? Normal HRV by Age and Device

A good HRV is one that is normal for you and holds steady or rises against your own baseline over weeks. There is no single healthy number, because heart rate variability falls with age and differs between devices. As a rough guide, the middle half of 25-year-olds in WHOOP's member data sit at about 45 to 100 ms overnight, and 45-year-olds at about 30 to 60 ms.

Here is what a careful lab study found for average HRV by age. These are means from 1,906 healthy adults in Germany, measured with a 5-minute ECG while lying down after a rest,^[2] so they run lower than the overnight averages most wearables show:

To see where your own reading lands, use the HRV by Age tool. It asks for your age, your device and your number, tells you whether your device reports RMSSD or SDNN, and places your reading against published age-based reference values, so you are not judging an Apple Watch number against a chart built for a ring.

Wearable data runs higher than the lab table. Across WHOOP members, the average overnight HRV is 65 ms for men and 62 ms for women. The middle half of 25-year-old men sit at about 50 to 100 ms, falling to about 35 to 60 ms at 45, and women of the same ages sit at about 45 to 90 and 30 to 55 (WHOOP member data).

What HRV actually measures

Your heart does not beat like a metronome. At 60 beats a minute, some beats come slightly less than a second apart and others slightly more. HRV is how much those gaps vary, measured in milliseconds. That variation is steered by your autonomic nervous system: higher HRV generally reflects more rest-and-digest (parasympathetic) influence, and lower HRV reflects more fight-or-flight (sympathetic) activity, as Garmin's HRV guide puts it. If the stress side of that system is new to you, the fight or flight response explains what it does in the body.

Two calculations show up on consumer devices:

• RMSSD (root mean square of successive differences) looks at how much each gap differs from the next one. WHOOP and Garmin report RMSSD, averaged across your sleep.
• SDNN (standard deviation of normal-to-normal intervals) looks at how spread out the gaps are across the whole reading. Apple Watch calculates HRV as SDNN from short readings it takes in the background when you are still, by default about every four hours, according to Apple's heart rate white paper.

These are different numbers. An Apple Watch SDNN of 45 and a WHOOP RMSSD of 45 do not mean the same thing. The length and timing of the reading matter too: researchers warn that norms from 24-hour, 5-minute and shorter recordings are not interchangeable.^[3] If you wear an Apple Watch, does Apple Watch track stress covers how its HRV readings work in more detail.

What is a normal HRV by age?

The clearest pattern in every dataset is that HRV falls with age. The largest study to date pulled readings from more than 8.2 million Fitbit users and found that HRV dropped fastest between ages 20 and 40 and more slowly after that. It also found a strong daily rhythm, with HRV peaking between about 5 and 8 am and bottoming out in the late evening. At 6 to 7 am, women aged 40 to 41 averaged roughly 38 to 43 ms of RMSSD, depending on the Fitbit model.^[1]

The German lab study shows the same slide decade by decade, and it found that the differences between men and women faded in the oldest age groups.^[2]

The other thing these datasets show is how wide "normal" is. In the lab study, the spread around each average is roughly half the average itself: women aged 25 to 34 averaged 42.9 ms of RMSSD, give or take 22.8 ms.^[2] Two healthy 30-year-olds can sit at 20 ms and 65 ms. Oura's HRV guide says typical values run from under 20 to over 200 milliseconds, and WHOOP notes that the most common overnight HRV among its members is about 40 ms for men and 37 ms for women, below the averages, because a small group with very high HRV pulls the averages up.

So what counts as a good HRV for you?

A good HRV is a stable one that sits inside or a little above your own usual range. Population charts tell you whether your number is unusual for your age. Your own history tells you whether today is unusual for you, and that is the question that matters day to day.

Garmin's approach is a useful model even if you wear something else. It needs about three weeks of overnight readings to set your personal baseline range (for example, 33 to 45 ms), then checks your 7-day average against it. A 7-day average inside your range is "balanced"; outside it is "unbalanced"; well below it is "low"; and if your whole baseline drops below age-based standards, Garmin calls it "poor."

Here is how to read your own number:

Is higher HRV always better?

Mostly, but not always. Higher HRV is generally linked with fitness and good recovery, and across the Fitbit data more daily steps went with higher HRV, though the authors stress that this is a correlation, not proof that steps cause it.^[1] Two exceptions are worth knowing.

First, Garmin notes that HRV far above your personal baseline has been linked to functional overreaching, especially when training involves large amounts of low-intensity exercise. A sudden jump while you feel exhausted is not a reason to celebrate.

Second, irregular heartbeats can push the number up. Apple says SDNN may be influenced by non-normal beats when there are many of them, and the Fitbit study notes that RMSSD is sensitive to erratic beats.^[1] A surprisingly high HRV next to an irregular rhythm notification is a reason to see a doctor, not a fitness win.

If you want to move a low number up the safe way, how to improve HRV covers sleep timing, alcohol, breathing and training.

How each device reports HRV

Most devices fold HRV into a bigger score, such as Garmin's Body Battery, Oura's Readiness or WHOOP's Recovery. The Stress Score Checker explains what those combined numbers mean when you are not sure how much of the score is your HRV.

Track it

One HRV reading tells you very little. A few weeks of readings, next to a note about your life, tell you a lot. A simple routine:

1. Use one number from one device. The overnight or morning average is the most consistent. Look at it once in the morning, not throughout the day.
2. Write down your 7-day average every Sunday. That single weekly number smooths out the noise of bad nights.
3. Log the context next to it. Hours slept, drinks, hard workouts, illness and stressful days. The 60-second mental health check-in records mood, energy, stress, sleep and connection in one go, so after a month you can see whether your low-HRV weeks line up with how you felt.
4. Check your sleep debt. Short nights are the most common reason HRV slides. The sleep calculator adds up your week, and sleep debt explains how to pay it back.
5. Compare with your age once a month, not daily. Run your 7-day average through the HRV by Age tool to see whether your baseline itself is drifting.

If your HRV has been low for weeks and you also feel flat, irritable or exhausted, the number may be reflecting stress you already feel. The mood tracker is a quick way to see whether your mood follows the same curve.

When to talk to a doctor

HRV is a wellness signal. It cannot diagnose anything, and a low number on its own is not a medical problem. Talk to a doctor if:

• your HRV stays well below your usual range for two weeks or more and you cannot find a reason
• a low or erratic HRV comes with a racing or irregular heartbeat, shortness of breath, dizziness or new exhaustion that sleep does not fix
• your watch gives you irregular rhythm notifications
• you started a new medication and your numbers changed sharply

Chest pain or fainting needs emergency care, whatever your watch says. And if a low stretch comes with weeks of low mood, worry or burnout, a doctor or licensed therapist is the right next step; the burnout test can help you put words to what is going on before that appointment.

A number on a screen rarely tells you why the week felt heavy. If your HRV has been sliding and you want to work out what changed, say it out loud to Lovon, an AI coach you talk to by voice. Lovon does not see your watch data, so you tell it the number and what has been going on, and it helps you sort out which change to make first.