Random integer with specific range: values are getting greater then max value

I need an random integer in a specif range. The range is from 100 to screen height - 400.

So this is what I get, but why are there values greater then the max value?

for (var i = 0; i < 100; i++) {
    const   screenHeight = $(document).height(),
            max  = screenHeight - 400,
            min  = 100,
            y    = Math.floor(Math.random() * max) + min;

    console.log(max, y, y > max);
}