public static Quarter GetPrevQuarter(string quarterYear) { var qtr = Quarters.Find(q => q.QuarterDescription == quarterYear.Substring(0, 2)); var year = quarterYear.Substring(3); var prevQtrId = qtr.QuarterId - 1; if (qtr.QuarterId == 1) { prevQtrId = 4; year = (Convert.ToInt32(year) - 1).ToString(); } var preQtr = Quarters.First(q => q.QuarterId == prevQtrId); var qtrYr = preQtr.QuarterDescription + " " + year; return(new Quarter { MonthId = preQtr.MonthId, QuarterId = preQtr.QuarterId, QuarterDescription = preQtr.QuarterDescription, QuarterYear = qtrYr }); }