Wearables

Apple Watch Series 12 and Ultra 4: what is new and which one to buy

Both 2026 watches measure your heart rate every five seconds and add a daily readiness score. The Ultra 4 costs twice as much and lasts twice as long. Here is how to choose.

By the How To, Simply team · 1 October 2026 · 3 min read

In shops since

18 September 2026

Price (US)

Series 12 from $399, Ultra 4 from $799

Battery (normal use)

Up to 24 hours / up to 50 hours

Software

watchOS 27

Works with

iPhone 11 or later on iOS 27

Apple announced the Apple Watch Series 12 and the Apple Watch Ultra 4 on 9 September 2026. They share a new set of heart sensors and most of the new software. The differences are battery life, toughness, satellite messaging and price. This article is based on Apple's announcement and launch reporting, not on our own testing.

What is new on both watches

Heart rate every five seconds

Older Apple Watches checked your heart rate in the background every few minutes unless you started a workout. The new sensors take a reading every five seconds all day, according to Apple. Heart rate variability, the small changes in time between beats that reflect stress and recovery, is also measured far more often. More frequent readings give a fuller picture of your day, not a more medical one: a watch is still not a diagnostic device.

A readiness score

Each morning the watch gives a score from 0 to 10 based on your recent activity, sleep and vital signs, with a plain suggestion: Recover, Pace Yourself, Ready or Go For It. Garmin, Whoop and Oura have offered similar scores for years. Treat it as a hint, and trust how you feel when the two disagree.

Audio Intelligence

The watch can recognise sounds around you such as a doorbell or an alarm, identify music faster, and replay the last moments of what was said with Live Rewind. Siri Recap summarises what you missed.

The S11 chip and watchOS 27

Both run on the S11 chip with watchOS 27. The redesigned Health app adds a Longevity tab. Some of the smarter Siri features depend on an iPhone that supports Apple Intelligence.

How they differ

All figures are Apple's own. Battery life in particular depends on how many workouts you record and whether the screen stays on.

Which one should you buy?

• Series 12 if you want health tracking, notifications and payments on your wrist, and you are happy to charge once a day. It has the same new heart sensors as the Ultra for half the price.
• Ultra 4 if you hike, dive or run long distances, often go where there is no mobile signal, or simply do not want to charge every night. The larger case does not suit small wrists, so try one on first.
• Keep your current watch if you have a Series 10 or 11 and are satisfied. watchOS 27 brings much of the new software to recent models; the five-second heart readings need the new sensors.

Before you buy

An Apple Watch needs an iPhone. Apple lists an iPhone 11 or later, or an iPhone SE from the 2nd generation, on iOS 27. To check your phone, see how to check your iOS version, and for what the update brings, our iOS 27 overview.