DateOnly Between methods

dateonlybetween.cs

public static int DaysBetween(DateOnly startDate, DateOnly endDate)
{
    return endDate.DayNumber - startDate.DayNumber;
}

public static (int Months, int Days) MonthsAndDaysBetween(DateOnly startDate, DateOnly endDate)
{
    int months = (endDate.Year - startDate.Year) * 12 + endDate.Month - startDate.Month;
    DateOnly testDate = startDate.AddMonths(months);

    if (startDate <= endDate)
    {
        if (testDate > endDate) months--;
    }
    else
    {
        if (testDate < endDate) months++;
    }

    int days = DaysBetween(startDate.AddMonths(months), endDate);
    return (months, days);
}

public static (int Years, int Months, int Days) YearsMonthsAndDaysBetween(DateOnly startDate, DateOnly endDate)
{
    (int months, int days) = MonthsAndDaysBetween(startDate, endDate);
    int years = months / 12;
    months %= 12;
    return (years, months, days);
}