Apple's accuracy article puts most bad heart readings down to fit and settings, not the sensor. Wear the watch snug, on the top of the wrist, with the sensor close to the skin, tighter for workouts and looser afterwards. Wrist Detection must be on in the Watch app under Passcode, or background readings such as resting and walking rates are not taken. Heart Rate must be on under Privacy.
Choose the workout that matches what you are doing so the watch picks the right inputs. Apple lists what else changes readings: skin perfusion, which drops in the cold; some tattoos, whose ink can block the sensor's light; and motion, since steady running and cycling read better than tennis or boxing. If you cannot get a steady reading, pair a Bluetooth chest strap. Calibrating the watch outdoors improves distance, pace and calorie accuracy but not the optical reading itself.
Differential
Likely causes of “Apple Watch heart-rate readings are missing or inaccurate”, and how to tell them apart
- 1
The band is too loose or the watch sits too low on the wrist
What separates it The readings drop out or jump during a workout because the band is too loose or the watch sits too low
How to confirm Snug the band for exercise and wear it on top of the wrist
- 2
Wrist Detection or Heart Rate privacy is off
What separates it There are no background or resting readings because Wrist Detection or Heart Rate privacy is off
How to confirm Turn on Wrist Detection under Passcode and Heart Rate under Privacy in the Watch app
- 3
Cold skin or low perfusion
What separates it There is no reading outdoors in winter because of cold skin or low perfusion
How to confirm Warm the wrist or use a chest strap, as Apple suggests
- 4
A tattoo under the sensor
What separates it The reading fails on one wrist but not the other
How to confirm Move the watch to the other wrist or use a chest strap
- 5
Irregular motion
What separates it The tennis or boxing readings are noisy because of irregular motion
How to confirm Use a Bluetooth chest strap for those sports
- 6
A dirty or scratched sensor window
What separates it The readings vary from day to day because of a dirty or scratched sensor window
How to confirm Clean the back of the watch with a dry lint-free cloth
Before you touch a setting
Record this first — changing settings destroys the evidence
- The model number and which heart sensor generation the model has
- Which reading fails: workout, resting, walking or on-demand
- What the watch was doing, the band tightness and which wrist
- Whether Wrist Detection and Heart Rate privacy are on
Try in this order
0 of 7 completedCheck the fit
ReversibleWear the watch snug on the top of the wrist, tighter for workouts and looser afterwards.
Turn on Wrist Detection
ReversibleTurn on Wrist Detection, in the Watch app, under My Watch, Passcode, and make sure that Wrist Detection is on.
Turn on Heart Rate
ReversibleTurn on Heart Rate, in the Watch app, under Privacy, and make sure that Heart Rate is on.
Pick the right workout
ReversibleChoose the workout type that matches what you are doing, or Add Workout for one not listed.
Clean the sensor
ReversibleClean the sensor, by wiping the back of the watch with a dry lint free cloth.
Calibrate outdoors
ReversibleCalibrate outdoors, by walking or running outdoors for about 20 minutes using Apple's calibration steps.
Compare with a chest strap
ReversiblePair a Bluetooth chest strap to see whether the fit or the sensor is at fault.
Model-specific
What is true of this model and not of its siblings
- Sensors by model
- Apple's tech specs: a third-generation optical heart sensor and electrical heart sensor on the Series 10, Series 9, Ultra and Ultra 2; a third-generation optical sensor with ECG on the Series 8 and 7; a second-generation optical sensor without ECG on the SE 2.
- Temperature and sleep features
- Apple's tech specs list temperature sensing on the Series 9, Series 10 and Ultra 2, and sleep apnea notifications are on the Series 9 and later and the Ultra 2 and later.
- Repair cost
- Fit and settings changes cost nothing. A chest strap is an optional extra of a few tens of dollars. A cracked sensor window or a dead sensor is a service repair: Apple's out-of-warranty battery service is $99, and launch-day repair fees ran from $199 for an SE 2 to $499 for an Ultra, per MacRumors.
- Other models this page answers
- These steps also fit models Apple Watch Ultra 2, Apple Watch Ultra, Apple Watch Series 8, Apple Watch Series 7, Apple Watch SE (2nd generation), Apple Watch Series 6.
Stop boundary
When this stops being a self-service repair
- !If the sensor window is cracked or readings are absurd on both wrists, book Apple service
- !If you have symptoms, contact a doctor before troubleshooting the watch
- !If a chest strap agrees with the watch, the fit is the fix, not the sensor
Evidence ledger
Sources behind this answer
Fit, Wrist Detection, Privacy setting, tattoos, skin perfusion, motion and chest straps.
Outdoor calibration for distance and calories.
The second-generation optical sensor on the SE 2.
Third-generation optical sensor and electrical heart sensor.
The Apple Watch line and its generations.
Exact questions
Common questions
Why is my heart rate missing during a run?+
Usually a loose band or the sensor losing contact. Snug the band and wear it on top of the wrist.
Do tattoos affect readings?+
Apple says the ink, pattern and saturation of some tattoos can block light from the sensor.
Why does the cold stop readings?+
Apple says skin perfusion, the blood flow through the skin, can be too low in the cold for the sensor to read.
Do all watches have the same sensor?+
No. Apple lists a third-generation optical sensor on the Series 10, Series 9, Ultra and Ultra 2, and a second-generation optical sensor on the SE 2.
Which models have the ECG?+
Apple says the ECG app is on Series 4 and later, not the SE. The Ultra, Ultra 2 and Series 6 to 10 have the electrical heart sensor.
Can I use a chest strap?+
Yes. Apple says you can connect a Bluetooth chest strap for a consistent reading.
Does calibration fix heart rate?+
No. It improves distance, pace and calorie accuracy, and helps when GPS is limited.
Do I need Wrist Detection?+
Yes for background readings such as resting and walking rates, and for Stand progress.
Which workouts read best?+
Apple says rhythmic movement such as running or cycling gives better results than tennis or boxing.