You can use a second laptop as a monitor if both machines support the right connection method

Using another laptop as a second monitor is possible, but it requires either software that mirrors your display or a hardware adapter that treats the second laptop's screen as an input device. Most laptops cannot accept video input the way a traditional monitor does — their video ports only send signals out, not receive them. This means you cannot straightforward plug an HDMI cable from your main computer into your second laptop and expect it to work.

The practical routes are software-based screen sharing (which works over WiFi or USB) or a hardware solution using a USB video capture card. Software is simpler and works across Windows, Mac, and Linux machines. Hardware adapters are less common but work if your second laptop has a USB-C port that supports video input — a feature found on some newer models but not all.

Key Takeaways

  • Most laptops cannot receive video input through their ports, so you need either software or a USB video capture card to use one as a monitor.
  • Software solutions like Spacedesk (Windows to Windows), Luna Display, or built-in screen sharing work over WiFi or USB and are the easiest route for most people.
  • Your second laptop must stay powered on and connected to the same network, and performance depends on your WiFi speed and the age of both machines.
  • USB video capture cards work only if your second laptop has a USB-C port that supports video input — check your laptop's manual or manufacturer specs before buying.
  • Lag and display quality will be noticeably worse than a wired monitor, especially over WiFi, so this works best for email, documents, and web browsing rather than video editing or gaming.

Using software to share your screen over WiFi or USB

The easiest method for most people is software that streams your main laptop's display to the second one. Spacedesk is free and works well for Windows machines sending to Windows, Mac, or Linux. read it on both laptops, install the server software on your main machine and the viewer on the second one, connect them to the same WiFi network, and the second laptop's screen will show your main display. The setup takes about five minutes.

If you own a Mac, Luna Display is a popular option, though it costs around $50 and requires a USB-C port on both machines. It works over WiFi or USB and has lower lag than most software solutions. For a free Mac-to-Mac option, you can use macOS's built-in screen sharing: go to System Preferences > Sharing on your main Mac, enable Screen Sharing, then on the second Mac open Finder > Go > Connect to Server and enter your main Mac's network address.

Software solutions work best when both laptops are on the same WiFi network and relatively close to your router. If your WiFi is slow or congested, you will notice lag when moving your mouse or scrolling. USB connections (available with some software like Spacedesk) are faster and more stable than WiFi but require a USB cable between the two machines, which limits how far apart they can be.

Using a USB video capture card if your laptop supports video input

A USB video capture card is a small adapter that converts video signals into USB data your second laptop can read. You connect an HDMI or DisplayPort cable from your main laptop to the capture card, then plug the card into a USB port on your second laptop. The second laptop treats the incoming video as a USB camera input, which some software can then display full-screen.

This method only works if your second laptop has a USB-C port that supports video input — a feature called USB-C alt mode or Thunderbolt 3. Not all laptops have this. Check your second laptop's manual or the manufacturer's website to confirm before buying a capture card. Popular capture cards include the Elgato Cam Link 4K and the AVerMedia Live Gamer Portable 2 Plus, which cost between $80 and $150.

Once the hardware is connected, you may need to install driver software on your second laptop so it recognizes the capture card. After that, open video software like OBS Studio (free) or your laptop's built-in camera app and select the capture card as the input source. The video will then display on your second screen. This method has less lag than WiFi-based software but requires the right hardware and more setup steps.

What to expect in terms of performance and lag

Using a second laptop as a monitor will never feel as responsive as a wired external monitor. WiFi-based software solutions typically have a delay of 100 to 300 milliseconds between moving your mouse on the main laptop and seeing the movement on the second screen. This is noticeable but tolerable for email, spreadsheets, and web browsing. For video editing, photo work, or gaming, the lag becomes frustrating.

USB connections and capture cards reduce lag to 30 to 100 milliseconds, which is closer to real-time but still not identical to a direct monitor. The age of both laptops, the speed of your WiFi, and how much other traffic is on your network all affect the actual lag you experience. A newer laptop with WiFi 6 will perform better than an older machine on WiFi 5.

Display quality also depends on your method. Software solutions compress the video to send it over your network, so the second screen may look slightly softer or less sharp than your main display, especially if you are viewing text or detailed graphics. Capture cards preserve more detail but still compress slightly. If you spend hours reading text on the second screen, a traditional monitor will be easier on your eyes.

Setting up your workspace with a second laptop as a monitor

Once your second laptop is displaying your main screen, position it at a comfortable viewing angle next to or above your main laptop. You will still use your main laptop's keyboard and trackpad (or an external keyboard and mouse) to control both displays — the second laptop is purely a display device and does not receive keyboard input.

In your main laptop's display settings, you can choose whether the second screen extends your desktop (so you can drag windows between them) or mirrors your main display (so both show the same thing). For most people, extending the desktop is more useful — you can keep email on the second screen while working on documents on the main one. Go to Display Settings on Windows or System Preferences > Displays on Mac and select "Extend" or "Arrange Displays".

Keep your second laptop plugged into power while using it as a monitor. Running the display software drains the battery quickly, and you do not want the second screen to shut down mid-work. Also make sure both laptops stay connected to your network — if the second one loses WiFi, the display will freeze or disconnect.

Troubleshooting common problems

If the second laptop does not appear in your software's device list, check that both machines are on the same WiFi network and that any firewall software is not blocking the connection. Restart both laptops and the software, then try again. If you are using USB, make sure the cable is plugged in fully and that you have installed any required drivers.

If the display is laggy or freezes, move your main laptop closer to the WiFi router or switch to a USB connection if your software supports it. Close other programs on both laptops that might be using bandwidth or processing power. If you are using a capture card and the video does not appear, check that the card is recognized in your second laptop's Device Manager (Windows) or System Report (Mac) and that you have installed the latest drivers from the manufacturer.

If the second screen goes black or disconnects frequently, the WiFi connection may be unstable. Try restarting your router or moving the second laptop closer to it. Some software also has a reconnect button in its settings — try clicking that before restarting everything.

When a second laptop makes sense versus buying a monitor

Using a second laptop as a monitor works if you already own the second machine and do not mind the lag and setup complexity. If you are buying a display specifically for this purpose, a traditional monitor is cheaper, faster, and easier. A basic 24-inch monitor costs $100 to $200 and plugs in with a single cable — no software, no WiFi, no lag.

A second laptop as a monitor makes sense if you travel frequently and want a portable second display, or if you have an old laptop sitting unused and want to give it a second life. It also works if you need a display for occasional use and do not want to invest in hardware. For daily work, especially if you spend hours at your desk, a dedicated monitor is the better choice.

Frequently Asked Questions

Can I use a tablet as a second monitor instead of a laptop?

Yes, tablets work the same way as laptops — you use software like Spacedesk, Luna Display, or built-in screen sharing to stream your main computer's display to the tablet. Tablets are lighter and more portable than laptops, so they can be a better choice if you travel or want something easier to position on your desk.

What if my second laptop is a Mac and my main one is Windows?

Spacedesk works from Windows to Mac, so you can use it in that direction. Some other software like Luna Display also supports cross-platform use. Check the software's system requirements before downloading to make sure it supports your specific combination of operating systems.

Will using a second laptop as a monitor drain its battery quickly?

Yes, running display software uses significant power. Keep your second laptop plugged into a power outlet while using it as a monitor. If you unplug it, expect the battery to last two to four hours depending on the software and your laptop's age.

Can I use a second laptop as a monitor if they are on different WiFi networks?

Most software requires both machines on the same network. If they are on different networks, you can sometimes use a VPN or remote desktop software like TeamViewer, but this adds complexity and usually increases lag. For the best experience, connect both to the same WiFi network.

Is there any way to reduce the lag when using software screen sharing?

Use a USB connection instead of WiFi if your software supports it — this cuts lag significantly. Move your main laptop closer to the WiFi router, close other programs using bandwidth, and make sure both laptops are relatively new. Older machines process the video stream more slowly, which increases lag.