Whoop: What the Research Says About Each Metric
Whoop builds almost everything around one number, the Recovery Score, and doesn't surface most of its underlying metrics as standalone readings.
Whoop's approach is the opposite of Apple's. It's synthesis without much standalone breadth. Most of what Whoop measures feeds directly into one composite Recovery Score rather than being shown as an individual number a user checks on its own. Below is what independent research and Whoop's own methodology documentation say about how that score is built, plus what Whoop tracks separately and what it's still working toward.
How Is Whoop's Recovery Score Actually Calculated?
Whoop's Recovery Score is a 0-100 composite built from HRV, resting heart rate measured during the night's deepest sleep, respiratory rate, sleep, skin temperature, and blood oxygen. HRV is described as the single most influential input; an independent analysis found HRV alone accounts for roughly 56 percent of the variance in a Recovery Score.
What Whoop calls it
"Recovery Score." Unlike Apple, Whoop doesn't display a standalone HRV or resting heart rate number prominently in its main interface. Both exist as inputs feeding the composite, which is the number Whoop actually wants a user to look at each morning.
Worth knowing
A real peer-reviewed evaluation found that composite recovery scores including Whoop's, Oura's Readiness Score, and Garmin's Body Battery are not methodologically equivalent to each other, despite similar-sounding names and overlapping inputs. The same person's Whoop Recovery Score and Oura Readiness Score on the same day are not directly comparable, even though both claim to measure the same underlying question.
How Does Whoop's Stress Monitor Work?
Stress Monitor gives a real-time score from 0 to 3, built from heart rate and HRV, using a log-transformed RMSSD calculation, compared continuously against a person's own 14-day baseline. Whoop factors in motion to separate physical exertion from psychological stress, and notifies a user when the score climbs, with breathwork exercises offered directly in the app.
What Whoop calls it
"Stress Monitor," a real-time complement to the once-daily Recovery Score. Both draw on the same underlying HRV and resting heart rate signals but operate on different timescales, one continuous through the day, one calculated fresh each morning.
How Does Whoop Score Sleep?
Whoop's Sleep Performance score is built from four inputs: sleep sufficiency (hours slept against hours needed), sleep consistency compared against the prior four nights, sleep efficiency, and a sleep stress measure.
What Whoop calls it
"Sleep Performance," a distinct framing from Oura's stage-architecture-heavy Sleep Score or Garmin's stress-augmented version. Whoop's formula weighs consistency across recent nights more heavily than either competitor.
How Does Whoop Calculate Strain and Calories?
Whoop's Strain and calorie estimate are heart-rate-based, built on a real, named formula from 2005 predicting energy expenditure from heart rate, body weight, and age, with proprietary adjustments layered on top.
What Whoop calls it
"Strain," Whoop's replacement for the step-count-and-active-calories framing every other brand uses. There is no standalone step counter presented as a primary metric the way Apple's Activity Rings or Fitbit's step count are.
Does Whoop Track Blood Oxygen and Skin Temperature?
Yes, since the 4.0 hardware generation. A pulse oximeter estimates blood oxygen saturation using red and infrared light absorption, useful context during sleep or altitude training, and a paired skin temperature sensor tracks nightly changes against a personal baseline. Both feed into the Recovery calculation alongside HRV and resting heart rate.
What Whoop calls it
"Blood Oxygen" and "Skin Temperature," both surfaced in the Health Monitor alongside heart rate and respiratory rate. Whoop doesn't report a standalone daytime SpO2 spot-check the way Apple's or Garmin's on-demand modes do; it's an overnight-only reading here as well.
What Is WHOOP Age, and How Is It Calculated?
WHOOP Age estimates physiological age using six months of sleep consistency and duration, daily steps, time spent in each heart-rate zone, strength-training time, VO2 max, resting heart rate, and lean body mass. It's framed as an "effective age," the age at which someone else would carry the same all-cause mortality risk, anchored to published mortality research. A separate "Pace of Aging" score, updated weekly and ranging from -1x to 3x, shows how quickly that number is currently moving.
What Whoop calls it
"WHOOP Age" and "Pace of Aging," part of the broader "Healthspan" feature set. It's a proprietary composite built from several individually-studied inputs (VO2 max, resting heart rate, sleep), but no independent peer-reviewed validation of the composite WHOOP Age estimate itself was found during research for this page.
What Whoop Doesn't Do (Yet)
Two real limitations worth knowing, one permanent, one in progress.
No ECG feature
Whoop's band form factor doesn't include an electrocardiogram sensor, unlike Apple's Watch or Fitbit's Sense 2.
No shipped CGM integration
Unlike Oura, which launched a live continuous glucose monitoring integration with Dexcom's Stelo sensor in 2025, Whoop has publicly discussed exploring glucose tracking but had not shipped an equivalent integration as of this writing.
If you want one clear daily number and don't mind the underlying metrics staying mostly in the background, Whoop's synthesis-first design is built for exactly that. If you'd rather see each metric on its own before any score combines them, Apple's more granular approach shows more of its work.