The b-score is the number your strap doesn’t have: strain, recovery, sleep and stress all describe what your day cost your body, and none of them say what the hours bought. The b-score is that measurement — per event, 0 to 100, while the day is still happening.
What does the number mean?
Each event on your calendar gets its own score and its own curve. A high b-score means the hour held your attention and moved you — as measured from your body, not from a rating you typed. A low one means the hour merely happened to you. Across a day, the pattern is the point: which meetings, workouts, and dinners were worth their spend, and which are furniture.
The name is lowercase — b-score — the way the app’s name is lowercase: brainful.
How is it different from strain or a stress score?
Those metrics read activation — heart rate up, variability down, the body allocating resources. Activation is a receipt: it proves something happened and tells you what it cost. It cannot tell whether the spending was worth it, because from the cost side your best hour and your most wasted one can look identical.
The b-score is aimed at the other quantity. Activation means something happened. The b-score means something mattered.
Where does the science come from?
From roughly twenty-five years of neuroscience on how the brain’s valuation of an experience shows up in the body. Dopamine and oxytocin — attention and emotional resonance — act on the heart through the nervous system, and their effects leave a readable signature in the heart’s rhythm. brainful reads the effects of those chemicals, not their levels, second by second. In a 2024 peer-reviewed study, that continuous cardiac signal identified the days people rated as low-mood with 90% accuracy.
The calendar supplies the other half: context. A signal with no context leaves you reconstructing the day from memory; a b-score arrives already attached to the event it describes — no journalling, no self-report.
What do you need to use it?
An iPhone, a Whoop strap (4.0 or later) you actually wear, and a calendar. In the Whoop app, turn on Heart Rate Broadcast; pair once in brainful; done. It runs alongside the Whoop app and changes nothing about how you use Whoop — no Whoop login, no API access to your account.
Privacy is architectural rather than promised: your heart rate is never stored — it is scored in the moment and discarded — and your scores and calendar never leave the phone. There is no account server. The only permissions it asks for are Bluetooth, Calendar, and Notifications.
The b-score is the missing metric for Whoop: your strap already tells you what the day cost. brainful tells you what it was worth.
Sources: Merritt, S. H. & Zak, P. J. (2024), “Continuous remote monitoring of neurophysiologic Immersion accurately predicts mood,” Frontiers in Digital Health; WHOOP Support, “Heart Rate Broadcast.” brainful is not a medical product, and nothing here is medical advice.