The latest macOS updates, which can include updates to Boot Camp Assistant. You will use Boot Camp Assistant to install Windows 10.
64GB or more free storage space on your Mac startup disk:
An external USB flash drive with a storage capacity of 16GB or more, unless you're using a Mac that doesn't need a flash drive to install Windows.
A 64-bit version of Windows 10 Home or Windows 10 Pro on a disk image (ISO) or other installation media. If installing Windows on your Mac for the first time, this must be a full version of Windows, not an upgrade.
To install Windows, use Boot Camp Assistant, which is included with your Mac.
Open Boot Camp Assistant, which is in the Utilities folder of your Applications folder. Then follow the onscreen instructions.
When Boot Camp Assistant finishes, your Mac restarts to the Windows installer. If the installer asks where to install Windows, select the BOOTCAMP partition and click Format. In most cases, the installer selects and formats the BOOTCAMP partition automatically.
Unplug any external devices that aren't necessary during installation. Then click Next and follow the onscreen instructions to begin installing Windows.
After Windows installation completes, your Mac starts up in Windows and opens a ”Welcome to the Boot Camp installer” window. Follow the onscreen instructions to install Boot Camp and Windows support software (drivers). You will be asked to restart when done.
Restart, then press and hold the Option (or Alt) ⌥ key during startup to switch between Windows and macOS.
If you have one of these Mac models using OS X El Capitan 10.11 or later, you don't need a USB flash drive to install Windows:
To remove Windows from your Mac, use Boot Camp Assistant, not any other utility.
For more information about using Windows on your Mac, open Boot Camp Assistant and click the Open Boot Camp Help button.
1. If you're using an iMac (Retina 5K, 27-inch, Late 2014) or iMac (27-inch, Late 2013) or iMac (27-inch, Late 2012) with a 3TB hard drive and macOS Mojave or later, learn about an alert you might see during installation.
2. For example, if your Mac has 128GB of memory, its startup disk must have at least 128GB of storage space available for Windows. To see how much memory your Mac has, choose Apple menu > About This Mac. To see how much storage space is available, click the Storage tab in the same window.
3. These Mac models were offered with 128GB hard drives as an option. Apple recommends 256GB or larger hard drives so that you can create a Boot Camp partition of at least 128GB.