Most health apps show today's steps and last night's sleep. CalmTide shows the cumulative biological outcome of those behaviours — your estimated baseline cortisol and HPA-axis balance — as a trend you can actually move over 8 to 12 weeks. Built entirely from Apple Health, on your device.
CalmTide reads the metrics your Apple Watch already collects, weighs them against published exercise-and-cortisol research, and turns them into a single weekly HPA Balance Score — plus a daily read on whether today's cortisol is likely low, moderate, elevated, or high.
HRV (SDNN) is the single best non-invasive proxy for HPA-axis state. CalmTide tracks your rolling average — every drop nudges your estimated cortisol load up.
Deep-sleep shortfall and REM disruption raise next-day cortisol. CalmTide reads your sleep stages and weights deep sleep most heavily.
Zone 2 lowers baseline cortisol; stacked Zone 4–5 sessions spike it. CalmTide badges every workout as cortisol-reducing, neutral, or spiking — with acute-to-chronic ratio, monotony and strain in your workout history on Pro.
As little as five minutes a day has a measurable cortisol effect. CalmTide credits logged mindful minutes and includes two guided sessions — a cyclic-sighing exercise and a resonance-breathing pacer.
Resting and walking heart rate, respiratory rate, blood oxygen (SpO₂) and VO₂ max round out the picture as secondary stress and recovery signals — each now viewable on its own Insights card.
Light in the window after you wake helps anchor your morning rhythm. Connect SolGlow and its morning-sun data feeds straight into that component of your score.
Your live HPA Balance Score ring with a cortisol-vs-baseline read, one smart recommendation, a five-second daily check-in, and a daily protocol checklist topped by a “days on track” consistency strip. Recovery tiles now lead with how far each signal sits from your own baseline (“above usual · +12%”), and a tap starts the new resonance-breathing session.
Opens with a weekly HPA-balance hero, then reads your MET-minutes and zone distribution against both the research-backed 530/week target and your own 8-week norm — with a week-over-week delta. A session list badges every workout's cortisol effect — reducing, neutral, or spiking — so you can see exactly which sessions helped and which cost you.
The headline view: an 8-week estimated baseline-cortisol line against an optimal target trajectory, with annotated spikes (that stacked-HIIT week shows up here) and milestone markers like "HRV improved" or "Morning rhythm crossed 70." This is the anxiety-relevant signal most apps never show you. The full eight weeks, plus extended 60- and 90-day history, come with Pro.
Plus an Insights tab — with personalized benchmarks (Pro) that place your HRV and resting heart rate against normative ranges for your age and sex, plus cards for blood oxygen (SpO₂), walking heart rate, and time on your feet, a personal-average line and a healthy-range band on your charts, and your tagged days turned into at-a-glance comparison bars — alongside HRV history, sleep-architecture breakdowns, a sun-to-next-day-HRV correlation, noise-exposure trends, and VO₂ max as a long-term HPA-health proxy.
Version 1.7 keeps the 1.6 promise and pushes it into the corners 1.6 missed: a workout without heart-rate data is no longer scored as the easiest kind of training, training load is shown as figures instead of a verdict, and the daily check-in gains an optional drink count. It is with App Review now; this page will say so the day it is live.
A manually logged session, a third-party app that saves duration only, or a day the watch stayed home used to be credited as easy Zone 2 — the most favourable kind of training in the model. Those minutes still count toward your weekly dose, worked out from calories and capped so an unmeasured session can never out-score a measured one, but they claim no zone and no cortisol direction, and the Week tab tells you how many minutes came through without heart rate.
The acute-to-chronic card no longer files you under a coloured band. The paper behind those bands measured injuries in team-sport athletes, not stress hormones, so the card now shows your last 7 days against your 4-week base, a single reference mark at 1.0×, and monotony and strain as plain numbers. With no 4-week base to compare against it says so, instead of calling you optimal. Still Pro, still on the Week tab.
Tag a night with alcohol and a small stepper appears; leave it blank and the night is a normal alcohol night. Once you have enough nights on each side, Insights compares your own next-day resting heart rate and HRV after one drink against two or more — your numbers, both sample sizes shown, no score and no lecture. Nights without a count are left out, not assumed light. Nothing is read from or written to Health for this.
The Today card that draws the daily cortisol curve is now titled “The typical cortisol rhythm” — a population model, anchored to your wake time when your watch recorded one. When it didn't, the curve is education only: no invented wake time, no “you are here” marker, and nothing to scrub a clock time off.
Breathwork descriptions now say what the cited study measured — cardiac vagal activity, during the session — rather than promising to lower cortisol. Morning-light and sleep-timing tips describe how your body clock times the morning cortisol rise instead of promising to sharpen it. And the environmental-sound card no longer draws a “safe” line that the WHO guideline it cited never set for stress.
Two Home Screen widget check-ins on consecutive days without opening the app used to overwrite each other, breaking a streak through no fault of yours. The pending taps are now a queue, drained oldest-first, so both days are kept.
1.7 asks for no new Health permissions and changes nothing about what CalmTide reads or writes. It has been submitted to App Review; until it is approved, the version on the App Store is 1.6, described below.
A stress score is only worth the measurements under it. Version 1.6 tightens those: HRV read from the night you actually slept rather than a 24-hour average that mixed in your commute, sleep scored on regularity as well as hours, and a rule that runs through the whole app — anything CalmTide couldn't see leaves a gap in the picture, never a zero in your score.
Your daily HRV is now the average of the SDNN readings taken inside the night's sleep — not a calendar-day mean that folded in your commute and your workout. On a night the watch wasn't worn, CalmTide falls back to the day's readings and labels the number as an all-day average, rather than quietly changing what it means. Scoring and baselines use only the overnight figure, so a fallback night sits out a comparison instead of being compared against nights measured a different way.
How consistent your sleep timing is predicts more than how long you slept, so a steady wake time now counts toward your score — the Sleep Regularity Index takes 30% of the sleep component, split off the existing duration terms rather than piled on top. Under three nights of sleep timing leaves it unmeasured and renormalises the rest.
Awakenings, time awake in bed, and sleep efficiency — for the nights your sleep source actually records them. Nights without that detail are left out of the averages rather than counted as perfect.
The gap between the body clock you keep on work days and the one you keep on free days, measured from your mid-sleep point the way the chronobiology literature defines it. It needs at least two free nights and three work nights, and reports nothing below that.
It was never a measured cortisol awakening response, and it no longer claims to be. The number is a proxy blended from your wake time, your morning light and your sleep quality — which is what it always was. The trend milestone that predicted a mental-health outcome from that proxy is gone, and the sleep-regularity research note now states the mechanism instead of quoting depression, anxiety and mortality figures.
No daylight sensor, too few nights of sleep timing, a night the watch was charging — those now leave a gap in the picture instead of a zero in your score. Morning light is also counted in the window after you wake rather than across the whole day, so an evening walk no longer ticks a morning box.
1.6 asks for no new Health permissions. The read set shrank by one type — exercise time was being requested and never used — and nothing was added.
Your scores always raised the same question: what, specifically, is doing this? Version 1.5 answers it from your own data — patterns read the morning after, when the biology actually lands, a weekly retrospective that ranks exactly what moved your score in points, and a Practice hub with the right dose for the moment you're in. Compared across your own days, and never presented as cause and effect.
See what caffeine, alcohol, late meals and hard workouts did to your HRV, sleep and readiness the next morning — when the biology actually lands. Plus your strongest cortisol link, drawn from your own data.
After a few weeks of check-ins, see whether how you feel actually lines up with your sleep, HRV and training. It waits until it has enough days on both sides of a comparison before it says anything.
A weekly retrospective that ranks exactly what moved your score, in points — sleep, morning light, HRV, mindfulness, training load — this week against last.
Cyclic sighing and resonance breathing in 2, 5 or 10-minute doses, with a suggestion for the moment you're in: evening wind-down, post-workout reset, elevated load.
Log how you feel straight from the Apple Watch app — it lands on your phone through the same path as the Home Screen check-in widget, so your streak and your day stay in one place.
Tell CalmTide what you're working on — stress, sleep, or training balance — and today's recommendations reorder around it instead of treating every goal the same.
Your daily check-in can mirror to Apple Health as that day's State of Mind entry, and a mood you logged in Health fills in a check-in you missed. Optional, your own entry only, and it asks the first time you check in.
If you log caffeine to Apple Health, see what an after-2pm dose tends to do to the next morning's HRV — compared against your own earlier-cutoff days, and phrased as an association.
Export a full backup and restore it on any device from Profile → Your Data. Personal records for your longest streak, best HPA week and calmest morning. Calm Coach now leads with today's status, readiness and last night's sleep. Today reorders by time of day, notification taps open the screen they're about, and dozens of reliability fixes.
CalmTide writes exactly two things to Apple Health, both entered by you: a completed breathwork or resonance session, saved as Mindful Minutes, and — new in 1.5, optional — your own daily check-in, mirrored as that day's State of Mind mood. Everything else it reads stays read-only, on your device. Estimates remain wellness context, not a diagnosis.
SolGlow owns the sun: UV, vitamin D, and morning-light timing. CalmTide owns stress recovery: cortisol load and HPA-axis balance. Install both and they share a secure on-device container — no servers, no accounts — so each app gets smarter. Neither needs the other to work.
When SolGlow is connected, your morning-sun data feeds the morning-rhythm component of CalmTide's weekly score, and a new "Sun → next-day HRV" correlation appears in Insights — so you can see, in your own data, whether getting out in the morning actually steadies your nervous system.
Your HPA score and today's recommendation on your wrist, synced from the phone (scores on Watch are part of Pro) — and new in 1.5, you can check in with how you feel straight from the Watch instead of only reading it.
A Today-summary and HPA-ring widget for your Home Screen, plus circular, rectangular, and inline Lock Screen widgets — your trend one glance away.
A morning check-in that arrives around your usual wake time, post-hard-workout recovery nudges, a Sunday weekly summary, and an alert when two hard sessions stack up. Tapping one now opens the screen it's about — a wind-down cue opens the wind-down session.
Everything is computed on-device from Apple Health. No account, no analytics, and no health data ever leaves your phone.
CalmTide asks for the essentials on day one. Deeper metrics — including dietary caffeine — sit behind an optional “enable advanced metrics” prompt in Profile, and Apple Health's State of Mind has its own prompt, shown the first time you check in.
Scores are clearly labelled as estimates from published research — not a clinical cortisol measurement. CalmTide tells you what it can and can't know.
CalmTide's scoring models are informed by published research on exercise, recovery, and the HPA axis — including the dose-response relationship between training volume and cortisol, and the measurable cortisol effects of sleep, breathwork, and morning light.
CalmTide provides wellness estimates based on published exercise-physiology research. It is not a medical device and should not be used to diagnose or treat any condition. Read the deep dive on the science behind CalmTide.
Free to download and use every day. CalmTide Pro adds the full 8-week trend, extended 60- and 90-day history, the 7-day cortisol forecast, score & forecast widgets, scores on Apple Watch, advanced training-load analytics — acute-to-chronic ratio, monotony and strain — and Calm Coach, the optional on-device explainer. New in 1.5, Pro also opens the weekly retrospective, what your check-ins reveal, and caffeine timing.
Billed monthly, renews until you cancel. New subscribers get a 1-month free trial.
Billed yearly, renews until you cancel. New subscribers get a 1-month free trial.
A one-time purchase. Never renews, never expires — yours for good.
Every plan unlocks the same Pro features
The HPA Balance Score and today's cortisol read, one smart recommendation, the daily protocol and five-second check-in, guided cyclic-sighing and resonance sessions, morning-after patterns, personal records, quiet notifications — and a data-confidence indicator on every score, so you always know how much data sits under the number. Your data stays yours: export a full backup or restore it any time.
Subscriptions auto-renew until cancelled, and you can cancel any time in your Apple ID settings. New subscribers get a 1-month free trial; the price and any trial are shown before you confirm. No account required. Requires iOS 18.6 or later; Apple Watch (watchOS 11+) recommended. See the Privacy Policy and Terms of Use.
Now on version 1.5 — “What moves it.” See the update history →