What does WHOOP's HRV number mean?

WHOOP gives you one HRV value per night, in RMSSD, weighted toward deep sleep and the later part of the night. It feeds your Recovery score with resting heart rate and sleep. Green is 67 to 100 percent, yellow 34 to 66 and red 0 to 33.

Recovery is a summary, and HRV is one of the things in it. When Recovery surprises you, look at the HRV number underneath and compare it with your own last few weeks.

Why is my Recovery red when I feel fine?

Because Recovery measures your body, and feeling fine is a different signal. In 39 adults tracked for three months, how stressed or nervous people said they felt had no link with their overnight HRV.

WHOOP’s own research shows what usually drags it down. In 20,968 WHOOP members, one drink above your usual against one below came with HRV 3.8 ms lower in women and 3.3 ms lower in men, and resting heart rate about 2.4 to 2.8 beats a minute higher. In 14,689 members, a maximal workout ending two hours before bed came with HRV 8.3 ms lower than a light one.

So a red morning after a late night is the system working. A red week with no cause is the pattern to look into.

Why is my WHOOP HRV different from my Oura?

Both use RMSSD, so you’d expect them to match. They don’t, because they measure different parts of the night.

WHOOP weights its average toward likely deep sleep and later in the night. Oura averages its five-minute samples across the whole night. In a 2001 sleep lab study, cited by WHOOP’s own researchers, the breathing-linked part of HRV was 123.7 percent higher in deep sleep than in REM. A number that leans on deep sleep can come out higher than one that doesn’t, from the same heart on the same night.

Different sensors and processing add to the gap. Keep the two as separate histories.

A simple way to picture it

Think of measuring how calm a river is. You can average its whole length, rapids and all. Or you can lean on the slow, deep stretches where the water barely moves.

Oura averages the whole river. WHOOP leans on the deep stretches. Both are fair ways to measure, and they won’t give the same answer.

How does WHOOP calculate HRV?

WHOOP’s data science team lead explained it on WHOOP’s community forum in August 2025.

1. It measures all night. The strap times your pulse continuously while you sleep.
2. It cuts the night into overlapping windows. In WHOOP’s words, “we calculate HRV in overlapping 5-minute windows (stepping forward every 30 seconds) throughout your entire sleep.”
3. It removes time awake. Windows when you were awake are dropped.
4. It weights the rest. “The weights are higher for intervals that occur during likely slow-wave sleep,” and for windows later in the night.
5. It gives one value. WHOOP’s developer data has a single field for it in each Recovery, hrv_rmssd_milli, the night’s RMSSD in milliseconds.

The same post said older descriptions of HRV taken only during deep sleep are “a bit outdated.” So if you’ve seen it said that WHOOP uses only the last stretch of deep sleep, WHOOP says that’s no longer how it works.

One consequence: WHOOP’s data gives one HRV number per night, so it can tell you a night was low but not when in the night it dropped.

What do WHOOP’s words mean?

WHOOP’s public documentation doesn’t say how much each input counts toward Recovery.

How accurate is WHOOP’s HRV?

Moderate Good agreement with an ECG in two independent lab studies, with a real dispute about how to test it fairly.

Is it fair to test WHOOP against an all-night average?

The two studies above disagree a little, and the researchers argued about it in print.

Both sides agree WHOOP’s HRV is close to an ECG. The argument is over how close, and it shows how much a device’s choice of window changes the number.

What has WHOOP’s own research found?

WHOOP’s scientists publish studies on members’ data regularly. Most involve WHOOP authors, all use WHOOP data, and they compare each person with themselves.

• Drinks. 20,968 members: one drink above your usual against one below, HRV 3.3 to 3.8 ms lower. Drinking an hour earlier than usual, against an hour later, about 1.5 ms higher in women.
• Late hard workouts. 14,689 members, about 4 million nights: a maximal workout ending 2 hours after usual bedtime came with HRV 14.6 ms lower than a light one.
• Steadiness. About 2 million nights: you need at least five of seven nights to measure how much your HRV varies across a week, and it varies more with more drinking, less activity and shorter or irregular sleep.
• Sharing a bed. 11,733 members: nights sleeping with a dog, cat or child came with HRV 1.41 to 1.95 ms higher than nights without, and the authors called the effects small.

How should I use my WHOOP HRV?

1. Wear it the same way every night. Same spot, same fit.
2. Look past the color to the HRV. Track its 7-day average against your own usual range.
3. Check red days against the evening before. Drinks, a late hard session and a short night explain most of them.
4. Act on a week, not a day. If HRV sits below your range for a week with no cause, ease off and look for what changed.
5. Start fresh after a change. A new strap generation or a move to a new wear spot is a new measurement.

Track it in Gyroscope

Connect WHOOP and every night’s HRV lands in Gyroscope on its own, charted against your own normal, with your sleep, resting heart rate and drinks beside it. WHOOP’s RMSSD is kept apart from an Apple Watch’s SDNN and never averaged with it. See tracking it in Gyroscope.