The short answer

A 120 Hz display may report 118 or 119 Hz in a browser, or temporarily drop near 60 Hz. Causes include adaptive refresh policies, power saving, foreground state, browser scheduling and page load. Web tests usually estimate timing with requestAnimationFrame, so they reflect the frame opportunities available to the browser and cannot replace a high-speed camera, photodiode or professional instrument.

Watch the stable range, not one instantLet the test run, observe where most samples settle and compare the result with the perceived smoothness of scrolling and motion.

Where the difference comes from

Adaptive-refresh devices lower their rate for static content and raise it after touch or animation. Systems may limit frame rate during low battery, high temperature, screen recording, external-display use or power-saving mode. A 24, 30 or 60 fps video also does not gain new frames simply because the panel supports 120 Hz. Frame rate describes content generation; refresh rate describes the display's update capacity.

External displays are limited by port, adapter and cable bandwidth as well as resolution, color depth and HDR. A connection that supports high refresh at a lower resolution may not support the same rate at maximum resolution with HDR. Wireless casting, remote desktops and virtual machines expose transmission or composition timing and are poor ways to verify a physical panel's maximum rate.

Step-by-step check

  1. Confirm that high refresh or adaptive mode is selected in system display settings. Disable power saving and let the device return to a normal temperature.
  2. Use the device's built-in diagnostics or open the online refresh rate test. Keep the tab in the foreground and close screen recording and heavy applications.
  3. Wait for samples to stabilize. Scroll or touch lightly to wake adaptive high refresh, and do not judge from the first second or two.
  4. Use the motion and ghosting test, then cross-check with another major browser, the system interface or a high-frame-rate application.

When to contact support

If high refresh is enabled, temperature and battery are normal, and the system interface, multiple browsers and supported apps all remain locked to a lower rate with visible stutter, update and restart the device and reset relevant display settings. If the problem remains, contact technical support with the model, OS version, setting screenshots and reproduction steps. An issue limited to one site or browser is more likely software compatibility or frame limiting than panel hardware.

Whether high refresh is worth paying for also depends on workload, performance and battery life. Read Is a high refresh rate worth it? and the display buying guide.