Why doesn’t the number of images remaining shown in the frame counter match the actual number of images I’m able to take?

The number of remaining images shown in the frame counter is only an estimate based on a fixed file size. However, all images are compressed in the camera. The RAW files use a lossless compression algorithm (meaning that the compression does not, in any way, degrade image quality). Therefore, the actual size (in megabytes) of each image will vary depending on the subject, shooting conditions and shooting mode, which can all affect how well an image compresses.