Buying a used CPU or GPU is always a risk because you never know what you're going to get until you test the hardware. Luckily, checking if your CPU or GPU is overclocked is quite easy.
CPU-Z reports the CPU clock speed
Overclocking is the process of increasing a chip's clock speed beyond the manufacturer's default speed. For example, the Intel i9-10900K has a base clock frequency of 3.70 GHz and a boost clock frequency of up to 5.30 GHz. However, if you have the right cooling setup, you can overclock your PC with Intel XTU to bring the maximum frequency closer to 6 GHz.
Therefore, to determine whether the hardware is overclocked or not, you will need to compare its maximum clock frequency with the stock specifications.

CPU-Z shows live CPU performance so you can make this comparison. This is one of the best free benchmarking programs for Windows, and you can use CPU-Z to check if your CPU is overclocked:
- Launch the program and take note Core Speed, Multiplier and Bus Frequency of CPU are listed in section Clocksin the lower left corner.
- For reference, do a quick Internet search for your CPU and look up its maximum clock speed. For example, if you search for the maximum frequency of the Intel i5-10600K, the result will be 4.8 GHz.
- When viewing chip specifications in CPU-Z, multiply Bus Speed with the highest multiplier value listed in parentheses. For example, the image above shows the highest multiplier listed as 48. If we multiply this by the bus speed, we get a result of about 4800 MHz or 4.8 GHz.
- Compare the calculation result with the reference value you looked up previously. If the result exceeds the reference value, the CPU is overclocked.
In the example from the image above, the CPU is not overclocked and is running at default; Its maximum frequency is no greater than that of the original version.
- Download CPU-Z for Windows (Free)
GPU-Z can test GPU clock frequency
To check if the GPU is overclocked, you would do a similar comparison using other software.

TechPowerUp's GPU-Z is free software that shows your GPU specifications. GPU-Z displays the reference GPU's clock speeds next to the GPU's actual settings, allowing you to compare two GPUs.
Here's how to use GPU-Z to find out if your GPU is overclocked:
- The speed of the reference sample is given in the row starting with Default Clock. Default Clock is its base speed, while Boost shows its normal boost clock. These numbers are provided by the manufacturer. For example, the image above shows that the Nvidia GeForce RTX 3080 is expected to have a default clock of 1440 MHz and a boost clock of 1800 MHz.
- The GPU clock speed is right below, in the row starting with GPU Clock. GPU Clock lists the base speed of the GPU, while Boost displays GPU boost clock settings. For example, the image above shows that this GPU is currently set to a base frequency of 1440MHz and a boost frequency of 1800MHz.
- If the GPU Clock number exceeds the Default Clock number, the GPU is overclocked.
In the example from the image above, the Default Clock and GPU Clock values - and their corresponding Boost frequencies – are identical; Therefore, this GPU is running at default speed and is not overclocked.
- Download GPU-Z for Windows (Free)
MSI Afterburner can manage GPU overclocking
MSI Afterburner monitors GPU performance and has long been considered one of the best GPU overclocking tools to enhance gaming performance.

MSI Afterburner gives you a live overview of your GPU's status. For example, it will show you the current GPU speed, fan speed, and temperature, which will fluctuate depending on your PC's current load.
In section Clockcheck the values reported in Core Clock and Memory Clock. Values with value +0 mean nothing changed; in other words, these clocks are set at the default frequency. On the other hand, if a positive value is found in any cell, such as +100, it means an overclock has been applied.
It's worth noting that no two GPUs are identical, even if they have the same model number. It's likely that your GPU, even at factory settings, is running at a slightly lower or higher base frequency than those you find online.
This distinction is especially true with modern GPUs: They are designed to self-overclock on the fly by detecting the capabilities of the cooling solution. In the image above, note that Afterburner does not apply any overclocking settings. The default boost frequency of this particular GPU is 1800 Mhz, but it is currently operating beyond the default specifications.
So it's more important to pay attention to relative differences rather than exact numbers.
After checking whether the CPU or GPU is overclocked, you can decide to keep the settings as they are or return to the default speed. To a certain extent, safe overclocking to increase FPS is a free performance boost that anyone with an effective cooling solution can take advantage of. But it also comes with risks – overclocking can damage your hardware if you're not careful.