Titan scores your HRV and heart rate against your own history. That history is your baseline. Each score keeps its own baseline, built from the readings that score uses, so the Recovery screen, the Stress screen and the Vitals screen can show different baseline values for the same person on the same day.
01Which baseline each score uses
| Score or screen | Baseline | History needed |
|---|---|---|
| Recovery | Median overnight HRV and sleeping heart rate of your measured nights, 60 nights by default | 7 measured nights covering 25% of the window |
| Stress | Median daily average HRV and daily resting heart rate over a fixed 60 days | Readings on 36 of the 60 days |
| Battery | The same 60-day baselines as Stress | Readings on 36 of the 60 days |
| Vitals | Median of the period you pick on the Vitals screen | Readings on 7 days and 60% of the period |
| HRV Baseline and RHR Baseline on You | Median daily average HRV and daily resting heart rate over 60 days | Readings on 36 of the 60 days |
The median is the middle value, so one unusual night moves it very little.
02The Recovery baseline
Recovery compares last night with the measured nights before it. A measured night has both overnight HRV and a sleeping heart rate. Your baseline is the median of those nights within the Recovery window, which is 60 nights by default. Titan builds one baseline for overnight HRV and one for sleeping heart rate.
The baseline needs at least 7 measured nights, and those nights must cover at least 25% of the window. On the default 60-night window that means 15 measured nights. Until then, the Recovery screen reads "Not enough nights for a baseline" and Today has no Recovery score.
Each night uses only the nights before it, so tonight never changes an earlier night's baseline or score. Titan reads the history already in Apple Health, so if you have worn your watch to bed for weeks, Recovery has a baseline on your first day. How the Recovery score works covers how Titan scores a night against the baseline.
03The Stress and Battery baselines
Stress compares each 5-minute stretch of your day with your usual resting heart rate and usual HRV. Your usual resting heart rate is the median of Apple Health's daily resting heart rate over the last 60 days. Your usual HRV is the median of your daily average HRV over the same 60 days. Each needs readings on at least 36 of those days. Until both exist, Stress shows "Needs more days of heart rate and HRV for a baseline".
The 60-day window is fixed. No setting changes it, and it does not follow the Recovery window. Battery reads the same two baselines to decide how fast sleep charges it and how fast waking time drains it. See Stress score and Battery.
04How Vitals ranges differ
The Vitals screen shows HRV, resting heart rate, respiratory rate and blood oxygen. It has its own period picker with 7 Days, 30 Days, 60 Days and 6 Months, and it opens on 30 Days. For each vital, the baseline is the median of your daily values in that period. The shaded range covers the middle 60% of those days, the 20th to 80th percentile.
Blood oxygen is the exception. Its chart shades a fixed Normal 95 to 100% band and marks readings below 95% in red.
A vital needs readings on at least 7 days and on 60% of the days in the period before Titan draws a baseline and range. Changing the period changes the baseline and range on that screen only. It never changes Recovery, Stress or Battery. Read more in Vitals.
05The baselines on You
Tap your avatar on Today to open You. The Your Fitness card shows HRV Baseline and RHR Baseline tiles, each labeled with its window, such as "60 day baseline". These tiles use your daily average HRV and daily resting heart rate, like the Stress baselines. The Recovery screen compares overnight values instead, so its baselines can read differently from these tiles.
