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thorstenboer
User level: Level 1 (12 points)

Apple Watch Ultra 4 heart rate inaccurate with watchOS 27

Title: Apple Watch Ultra 4 (watchOS 27): false high heart rate at workout start, then minutes-long gaps – getting worse


Device: Apple Watch Ultra 4, watchOS 27.0 → 27.0.1, paired iPhone on iOS 27.0.1. Worn since 18 Sept 2026.


I have recorded 14 outdoor runs (easy pace, 6:20–7:50 min/km) and analysed the exported workout files second by second. The same pattern appears in almost every run:


1. False high values at the start: during the first 20–60 seconds the watch shows 120–155 bpm (13 of 14 runs). My real heart rate at that point is around 80–90 – the first plausible value after the gap is usually ~84, then rising normally to ~100–110.

2. Long gap right after that: no heart rate data at all for 2 to 11 minutes.

3. Many shorter dropouts during the rest of the run (20 s to 5 min).

4. Frozen values: in my latest run the watch showed exactly 140 bpm for over 30 seconds while I was standing still, and 165–166 bpm for 12 seconds at an easy pace – a few minutes later 82–101 at the same pace.


Share of seconds with a heart rate value, run by run: 84 % → 73 % → 43 % → 37 % → 19 % → 58 % → 74 % → 47 % → 47 % → 26 % → 18 %.


What I have tried:

- Band tighter, watch one finger above the wrist bone (helped once, not consistently)

- Outdoor Run workout, no external sensor paired


Interesting detail: my previous Apple Watch Ultra 2 showed the exact same false start values in all 3 runs after updating to watchOS 27.0 – but never in 2025 on watchOS 11. So I suspect at least the start problem is software-related, while the growing gaps may be specific to my unit.


Questions:

- Is anyone else seeing this on the Ultra 4 / Series 12 or on older watches with watchOS 27?

- Has a restart, re-pairing, setting up as new watch or an exchange fixed it for you?


Thanks for any experiences!

Posted on Oct 6, 2026 9:11 AM

8 replies

Ingo2711
User level: Level 10 (93,009 points)

Oct 6, 2026 11:18 PM in response to thorstenboer

This might be related to the newer Apple Watch models, have a look at this discussion:

Falsely High Initial Heart Rate Readings - Apple Community


I haven't seen this on my Ultra 2 during Outdoor Walks or Cycling Outdoor workouts, but I have to tighten my Training Loop a bit more than in watchOS 26 since the latest updates, to get a reading.


Which Watch band are you using? It works best if I use the Ocean Band during workouts.

pr0230
User level: Level 1 (20 points)

Oct 27, 2026 9:45 AM in response to pr0230

Follow up to my previous message. I am still having the same problem with OS 27.2. I am using the Workoutdoor app for walking. It seems the heart rate goes really high in the beginning and if I put the app on pause, it’ll jump down to where my actual heart rate is. From then on it seems to be accurate so one pause to adjust it back and then it seems to be OK.

thorstenboer Author
User level: Level 1 (12 points)

Oct 10, 2026 4:54 AM in response to thorstenboer

Update (10 Oct):

4 more outdoor runs after the restart:

- False start values every time: 123–138 bpm in the first minute (actual approx. 85–95)

- Then no data at all for 8–12 minutes (8.3 / 8.9 / 12.2 / 11.5 min)

- HR coverage: 44 % / 27 % / 7 % / 29 % (before the restart: 47 / 47 / 26 / 18 %)


When the watch does record after the gap, the values are plausible (90–110 bpm at an easy pace). A core workout without running showed no start error at all.


So far: start error in 17 of 18 runs, still on watchOS 27.0.1.


This is not about using a chest strap or similar – it's obvious that works fine.

It's about Apple's claim that made me upgrade from the Apple Watch Ultra 2 to the Ultra 4: that the sensor now measures heart rate every 5 seconds and is more accurate. Given this experience, the upgrade has been pointless for me.

salvatorefrombcn
User level: Level 1 (4 points)

Oct 14, 2026 11:11 PM in response to thorstenboer

I'm having the exact same issue. I previously used an Ultra 2 and same issue and gaps in heart rate tracking. Initially, my Ultra 4 worked perfectly (the Ultra 2 too), but after a recent update, the dropouts started. The only workaround that helps is stopping my walk or run and keeping my arm completely steady until the heart rate sensor picks up again. This shouldn't be happening—pausing is easy enough when walking or hiking, but it's really inconvenient when running.

Simone187k
User level: Level 1 (20 points)

Nov 3, 2026 11:44 AM in response to thorstenboer

I have a very similar issue to yours. I haven't tracked it with the same level of precision as you, but I can say for sure that when I start running, it often fails to measure my heart rate. I have to take it off, wipe away the little bit of sweat, and put it back on—only then does it start reading again.


Same thing during the run: it frequently either freezes on a specific value or stops reading my heart rate altogether for several minutes (so I have to stop, take it off, and clean it). This happens to me on the Ultra 4, and it used to happen on my Series 9 as well.

pr0230
User level: Level 1 (20 points)

Oct 23, 2026 4:32 AM in response to thorstenboer

I have the same problem. ultra 2 watch. 27.0.1… Have done forced reset, no help. Cleaned sensor. ALWAYS in the beginning… eventually smoothes out. Hope 27.2 fixes this but I’ve read others with 27.2 beta did not fix this problem.

salvatorefrombcn
User level: Level 1 (4 points)

Oct 27, 2026 10:00 AM in response to pr0230

I’ve updated as well, and I’m also experiencing issues with elevation gain. Since the update, it has been adding around 40–50 metres of extra elevation on urban routes that I walk every day and know very well, so I’m certain the calculations are incorrect.

Snow Tiger
User level: Level 1 (76 points)

Oct 15, 2026 2:59 AM in response to thorstenboer

I’ve always had dropouts with the heart rate from my first Apple Watch 2 to my Watch 12.

Originally posted at discussions.apple.com/thread/256371390