Find why MSFS loses FPS with two monitors, what Limited by MainThread means, and how to fix GPU load, pop-outs and second-monitor stutter.
Microsoft Flight Simulator usually loses FPS with two monitors because the second screen adds pixels, another 3D view, instrument pop-outs or competing GPU work—not simply because it is connected. If MSFS reports Limited by MainThread, reduce CPU-heavy views, traffic and detail; if it is GPU-limited, reduce resolution and graphics load.
This diagnosis applies to MSFS 2020 and MSFS 2024 on Windows PC. A static extended desktop normally has little effect; the performance cost depends primarily on what the simulator or another application displays there.
How much performance do you lose with two monitors?
There is no fixed percentage because a second monitor can add almost no rendering work or effectively require another complete scene. Resolution, display method, aircraft systems and the existing CPU or GPU bottleneck determine the result.
| Second-monitor use | Expected performance impact | Work being added |
|---|---|---|
| Static extended desktop | Usually negligible | Display scan-out, desktop composition and a small amount of video memory |
| Mirrored main display | Usually negligible to small | Output scaling or a changed resolution and refresh mode; MSFS does not normally render the scene twice |
| Browser, video or moving map | Small to noticeable | Video decoding, browser GPU acceleration, animation and desktop composition |
| Instrument or glass-cockpit pop-outs | Noticeable and aircraft-dependent | Avionics updates, detached windows and compositing |
| One wide MSFS view spanning both screens | Potentially large | More rendered pixels, with mostly GPU-side cost |
| Independent second 3D view | Often the largest loss | Another camera perspective, draw calls, terrain, objects and pixel rendering |
Pixel count explains part of the difference. One 3840 × 2160 view contains about 8.3 million output pixels; two such views contain about 16.6 million. FPS will not scale perfectly with that ratio because render scaling, upscalers and CPU limits alter the workload, while a separate camera adds CPU work that pixel arithmetic does not show.
Does connecting a second monitor alone reduce FPS?
Simply connecting a second monitor should not cause a substantial MSFS performance loss. If FPS falls sharply with nothing but a static desktop on that display, investigate resolution changes, refresh-rate behaviour, V-Sync, GPU routing, drivers and background software before lowering simulator settings.
Mirroring can make Windows select a display mode supported by both screens. On a desktop PC, connecting both displays to the same discrete graphics card is usually the simplest arrangement. A motherboard video port does not share MSFS rendering with the integrated GPU and may introduce cross-adapter copies, especially when simulator windows are moved between displays.
Why does MSFS 2024 or MSFS 2020 show Limited by MainThread?
Limited by MainThread means the CPU-side thread preparing simulation and rendering work is taking longer per frame than the GPU. An independent second view, busy glass avionics, traffic and detailed scenery can increase this work in both MSFS 2024 and MSFS 2020.
Total CPU utilisation may still look modest because one critical thread can determine the frame rate while other cores remain less busy. Lowering resolution will usually achieve little in this state; it reduces GPU work, not the main-thread workload.
- Remove independent 3D views first. This is usually the largest dual-monitor CPU saving.
- Reduce Terrain Level of Detail and Objects Level of Detail. These settings affect how much scenery the CPU must prepare.
- Cut traffic and airport activity. AI aircraft, road vehicles, ships and detailed ground activity can all add main-thread work.
- Reduce avionics refresh workload. Use a lower glass-cockpit refresh option when the simulator or aircraft provides one, and close panels that are not required.
- Test without CPU-heavy add-ons and companion applications. Traffic injectors, moving maps and utilities that repeatedly query simulator data can worsen an existing main-thread limit.
If the overlay instead shows Limited by GPU, prioritise the combined display resolution, render scaling, clouds, shadows and other graphics effects. An available upscaler may help a GPU limit, but it will not remove a main-thread bottleneck.
How do I fix dual-monitor FPS loss in MSFS?
A controlled comparison identifies whether the loss begins with the physical display, an application on that display or an additional MSFS render. A mistake we see constantly is changing several graphics and Windows settings together, which hides the actual cause.
- Establish a repeatable baseline. Use the same aircraft, airport, cockpit camera, weather and traffic. Let scenery loading settle, temporarily disable the second display in Windows and keep the simulator's render resolution unchanged.
- Enable an empty extended desktop. Connect or enable the second monitor without opening a browser, map, video, pop-out or simulator view. A large loss at this point indicates a display-mode, driver, compositor or GPU-routing problem.
- Add one workload at a time. Start the browser, video, moving map, instrument pop-out or second 3D view separately. The first item that causes the drop is the useful result.
- Read the simulator bottleneck. Enable Developer Mode and its FPS display, then compare the main-thread and GPU frame times. Keep frame generation unchanged during these tests because it can alter the displayed FPS without removing the underlying workload.
- Adjust the correct side. Reduce view count, traffic and level of detail for a main-thread limit. Reduce rendered pixels and graphics effects for a GPU limit. If video memory is full, reduce memory-heavy settings and close GPU-accelerated applications.
- Check the display chain. Confirm that Windows is using each monitor's intended resolution and refresh rate. Test both displays on the discrete GPU where possible; laptop output routing is model-dependent and may not be changeable.
- Repeat the same scene. Compare steady frame time as well as average FPS. A higher average with frequent spikes may feel worse than a slightly lower but consistent rate.
If the monitor test reveals a broader simulator bottleneck, use our MSFS 2024 bottleneck-by-bottleneck performance checklist or the equivalent MSFS 2020 FPS optimisation guidance rather than changing unrelated settings at random.
Why does the second monitor stutter when playing MSFS or other games?
Second-monitor stuttering often means the main game has consumed nearly all available GPU time, or Windows is struggling to pace two displays with different refresh behaviour. The simulator may remain smooth while video or animation on the secondary screen misses frames.
- Leave some GPU headroom. Cap MSFS below the rate it can normally sustain or reduce a GPU-heavy setting. A game holding the GPU at sustained full utilisation can starve browser animation and video composition.
- Stop animated content as a test. Pause video, moving maps, live wallpapers, capture previews and animated browser tabs. If the game immediately becomes smooth, the second monitor itself is not the cause.
- Test browser hardware acceleration both ways. Disabling it may help a GPU-limited system, but it transfers more work to the CPU and can worsen
Limited by MainThread. - Check focus-related limits. If MSFS slows only after clicking a window on the second screen, inspect background frame-rate caps in the graphics driver, recording software and overlays.
- Remove capture and overlay conflicts. Monitoring tools, streaming previews and recording applications can add both composition work and inconsistent frame pacing.
Should both monitors use the same refresh rate?
Two monitors do not have to use the same refresh rate, but matching them temporarily is a useful diagnostic test. Mixed-refresh configurations are most likely to expose stutter when the secondary screen contains video, animation or another hardware-accelerated window.
- Verify each display's actual refresh rate in Windows Advanced display settings; do not assume the advertised rate is active.
- Temporarily select the same refresh rate on both screens and retest the identical scene.
- Test V-Sync, variable refresh rate and frame caps one change at a time.
- If FPS suddenly locks to an exact fraction of the monitor refresh rate, suspect synchronisation or a frame limiter rather than a proportional loss of rendering power.
A falling FPS counter accompanied by sustained high GPU utilisation usually indicates genuine extra rendering load. Stable FPS with visible judder more often points to frame pacing, desktop composition or refresh interaction.
Why do MSFS pop-out instruments reduce FPS?
Instrument pop-outs cost performance because MSFS continues updating the avionics while Windows treats each detached display as another composited window. The loss varies substantially by aircraft because a complex glass cockpit requires more work than a simple gauge.
Moving an existing panel to the second monitor is not necessarily the expensive step; creating and continuously updating the pop-out is. Making it smaller may reduce some pixel and composition work, but it does not eliminate the instrument logic. Do not assume that moving it off-screen or minimising it stops the updates—close it and retest.
Keep only the panels you use, reduce their size and select a lower cockpit-display refresh option if one is available. Our detailed fixes for glass-cockpit pop-out FPS loss cover this specific workload.
Should I stretch MSFS across two monitors or use a separate view?
A single wide view is normally easier on the main thread, while an independent second view provides a more useful viewing angle at a higher CPU and GPU cost.
- Choose a static extended desktop for maps, checklists and controls when preserving simulator FPS is the priority.
- Choose one wide render when you want more horizontal view and can accept the increased pixel load and possible perspective distortion.
- Choose an independent 3D view when the second monitor must show a distinct direction or correctly angled side view, and the system has enough main-thread and GPU headroom.
- Choose instrument pop-outs for a home-cockpit panel, accepting that the aircraft's avionics complexity may determine the cost.
Our comparison of MSFS dual-monitor setup methods explains how these display arrangements differ before you commit to the most demanding option.
Will capping FPS fix two-monitor performance?
An FPS cap can improve consistency and leave GPU time for video or applications on the second screen, but it cannot restore rendering capacity already consumed by another MSFS view. Set the cap to a rate the system can sustain in demanding normal flying, not its highest rate in an empty scene.
Apply the cap after identifying the bottleneck. If MSFS is main-thread limited at 25 FPS, a 30 FPS cap will not make it reach 30; reducing CPU-side workload is the fix. If the system fluctuates between 45 and 60 FPS while GPU-limited, a sustainable lower cap may produce smoother frame pacing and fewer secondary-screen stutters.