diff --git a/WebContent/jsp/onl/kjb/statistics/apiStatsDayMan.jsp b/WebContent/jsp/onl/kjb/statistics/apiStatsDayMan.jsp
index ee499a4..fafa922 100644
--- a/WebContent/jsp/onl/kjb/statistics/apiStatsDayMan.jsp
+++ b/WebContent/jsp/onl/kjb/statistics/apiStatsDayMan.jsp
@@ -575,14 +575,31 @@
 			$("input[name=searchStartDateTime]").inputmask("9999-99-99", { 'autoUnmask': true });
 			$("input[name=searchEndDateTime]").inputmask("9999-99-99", { 'autoUnmask': true });
 
-			// 기본값 설정 (이번달 1일 ~ 오늘)
+			// 기본값 설정 (어제 기준 해당 월 1일 ~ 어제)
 			var today = getToday();
+			var todayStr = today.replace(/-/g, '');
+
+			// 오늘 날짜를 Date 객체로 변환
+			var year = parseInt(todayStr.substring(0, 4));
+			var month = parseInt(todayStr.substring(4, 6));
+			var day = parseInt(todayStr.substring(6, 8));
+			var todayDate = new Date(year, month - 1, day);
+
+			// 어제 날짜 계산
+			todayDate.setDate(todayDate.getDate() - 1);
+			var yesterday = todayDate.getFullYear() + '-' +
+				('0' + (todayDate.getMonth() + 1)).slice(-2) + '-' +
+				('0' + todayDate.getDate()).slice(-2);
+
+			// 어제가 속한 달의 1일 계산
+			var firstDayOfMonth = todayDate.getFullYear() + '-' +
+				('0' + (todayDate.getMonth() + 1)).slice(-2) + '-01';
+
 			if (!$("input[name=searchStartDateTime]").val()) {
-				var firstDay = today.substring(0, 8) + "01";
-				$("input[name=searchStartDateTime]").val(firstDay.substring(0, 4) + '-' + firstDay.substring(4, 6) + '-' + firstDay.substring(6, 8));
+				$("input[name=searchStartDateTime]").val(firstDayOfMonth);
 			}
 			if (!$("input[name=searchEndDateTime]").val()) {
-				$("input[name=searchEndDateTime]").val(today);
+				$("input[name=searchEndDateTime]").val(yesterday);
 			}
 
 			initCharts();