import math


def calc_full_fit_period(calibration_start_date, holdout_end_date,
                         time_divisor):
    """Calculates transactions period by time unit predictions.

    Args:
         calibration_start_date: Calibration start date.
         holdout_end_date: Holdout end date.
         time_divisor: Time divisor.

    Returns:
        Total number of periods to predict.
    """
    return int(
        math.ceil((holdout_end_date - calibration_start_date).days /
                  time_divisor)) + 3