Key takeaway: Shrinking your existing Windows partition from within Windows, before you ever start the Linux installer, is the safest way to make room for a dual-boot setup — always back up first.

Dual-booting lets you keep Windows and install Linux alongside it, choosing which one to start each time you turn on your PC. The part that makes people nervous is partitioning — dividing your drive's storage space between the two systems — but done carefully and in the right order, it is a very safe, well-understood process.

Before you start: Back up your important files before touching partitions, as described in our backup guide. While shrinking a Windows partition is normally safe, working from a full backup means nothing is ever genuinely at risk.

Step 1: Shrink your Windows partition first

The safest order is to create free space from within Windows itself before you ever run the Linux installer, since Windows' own tools are well tested for this exact job.

  1. In Windows, right-click the Start button and choose "Disk Management."
  2. Right-click your main Windows partition (usually C:) and select "Shrink Volume."
  3. Windows will calculate the maximum amount it can shrink by. Enter the amount of space, in megabytes, you want to free up for Linux — 40,000MB (about 40GB) is a reasonable minimum for a lightweight distribution with some documents and software, more if you plan to store a lot of files on the Linux side.
  4. Click "Shrink." This creates a block of "Unallocated" space on your drive, shown in Disk Management, which Windows itself will not touch.
  5. Do not format or assign a drive letter to this unallocated space — leave it exactly as unallocated. The Linux installer will use it during installation.

Step 2: Check Secure Boot and BIOS settings

Most modern beginner distributions (Linux Mint, Ubuntu, Zorin OS) work fine with Secure Boot left switched on, but it is worth confirming this for your specific chosen distribution beforehand, and knowing how to reach your BIOS or UEFI settings screen (usually a specific key such as F2, F10, F12 or Delete pressed right after powering on) in case you need to adjust boot order later.

Step 3: Install Linux into the free space

  1. Boot from your Linux installer USB drive (see our guide on creating one with Rufus or balenaEtcher).
  2. When the installer asks about installation type, choose the option along the lines of "Install alongside Windows" if offered — most beginner distributions detect the free space and offer this automatically, which is the simplest and safest route.
  3. If that automatic option is not offered, choose "Something else" or "Manual partitioning," and select only the unallocated free space you created in Step 1 — never select or modify your existing Windows partition.
  4. Within that free space, most guides recommend letting the installer create the necessary partitions automatically (a root partition and a swap area), which is fine for most home users.
  5. Confirm the installer is writing the bootloader (GRUB) to the correct drive — usually the default option is correct and will add a boot menu letting you choose Windows or Linux each time you start the PC.
  6. Proceed with installation, then restart and confirm the new boot menu appears, allowing you to choose between Windows and your new Linux installation.

Tip: Tools like GParted, included on most Linux installer USB drives, let you view your partition layout visually before committing to anything — use it to double-check you are about to install into the correct free space.

What to avoid

Never select "Erase disk and install" unless you genuinely intend to replace Windows entirely — this option deletes everything on the drive. Similarly, avoid manually resizing your Windows (NTFS) partition from within the Linux installer if you can help it; doing that shrink from Windows itself in Step 1 is more reliable and reduces the chance of file system errors.

Frequently asked questions

How much space should I leave for Linux?
At least 25-40GB for a lightweight distribution with modest software and documents; 60GB or more if you plan to store many files or install additional programs on the Linux side.
Will dual-booting slow down Windows?
No — Windows runs exactly as before when you choose it at the boot menu; the two systems do not interact with or slow down one another during normal use.
What if the boot menu doesn't appear after installation?
This usually means a BIOS boot order setting needs adjusting to prioritise GRUB; entering your BIOS/UEFI settings and checking the boot order typically resolves it.

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