def calculate_intensity_group(hfi: float) -> int:
    """ Returns a 1-5 integer value indicating Intensity Group based on HFI.
    Intensity groupings are:

    HFI             IG
    0-499            1
    500-999          2
    1000-1999        3
    2000-3999        4
    4000+            5
    """
    if hfi < 500:
        return 1
    if hfi < 1000:
        return 2
    if hfi < 2000:
        return 3
    if hfi < 4000:
        return 4
    return 5