The best way to know if an Apple Watch is compatible with your iPhone is to check out the iOS compatibility list on Apple’s website

All Apple Watches have been compatible with iPhone 5 (2012) or later, but this may change with future updates to both devices.

Here’s a breakdown of the Apple Watches compatibility with iPhones.

Not sure which Apple Watch model you have? Identify your Apple Watch (Apple.com)

Apple Watch First Generation

The first-ever Apple Watch is compatible with iPhone 5 or later. Your phone needs to be running iOS 8.2 or later.

Apple Watch First Generation
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Apple Watch Series 1 and Apple Watch Series 2

Apple Watch Series 1 and Apple Watch Series 2 are compatible with the iPhone 5 or later. Your phone needs to be running iOS 11 or later.

Apple Watch Series 3 

There are two variations of the Apple Watch Series 3: one with integrated cellular and the other without.

The Apple Watch Series 3 without cellular is only compatible with iPhone 6 or later. The watch comes with an included nano-SIM card that allows iPhone users to use cellular data services when there’s no Wi-Fi available.

The Apple Watch Series 3 with cellular works with all iPhones running iOS 14 or later. The watch can make and receive calls over Wi-Fi using your phone’s voicemail and number, and it can also send and receive text messages. 

Older versions of the Apple Watch Series 3 may run on an iPhone 6 with iOS 13, but that’s not guaranteed.

Apple Watch Series 3
Image source: businessinsider.com

Apple Watch Series 4

Apple Watch Series 4 also has two variants. The LTE version is compatible with the iPhone 6 or later, and the Non-LTE version can be used with an iPhone 5s.

Related: How to Update Your Apple Watch

Apple Watch Series 5

Apple Watch Series 5 requires an iPhone 6s or later. Your phone needs to have iOS 13 or later installed.

Apple Watch SE

You need an iPhone 6s or later running iOS 14 or later to use with the Apple Watch SE.

Apple Watch SE
Image source: businessinsider.com

Apple Watch Series 6

Apple Watch Series 6 requires an iPhone 6s or later. Your phone needs to be running iOS 14 or later.

To ensure there are no compatibility issues between your Apple Watch and your iPhone, make sure both devices run the latest version of the OS. 

Apple Watch Series 6
Image source: businessinsider.com