Although in this case Forest Stats shows 850k estimated render items, the value is obviously not exact because your render is exceeding 5 Mill.
Are you rendering a moving camera ? Unfortunately, it's not possible to know the total number of items when using Camera clipping on an animated view, because the distribution changes at each frame.
I suggest to enable Camera->Distance falloff, so the number of items will keep much more constant. Probably you must make some rendering tests before, adjusting Fallof Scale to make the distant items tiny. If not, you would get flickering, because the distribution changes with the camera's movement.