diff --git a/src/main/kotlin/kr/co/vividnext/sodalive/chat/character/service/RankingWindowCalculator.kt b/src/main/kotlin/kr/co/vividnext/sodalive/chat/character/service/RankingWindowCalculator.kt
index 8057d85..56dad23 100644
--- a/src/main/kotlin/kr/co/vividnext/sodalive/chat/character/service/RankingWindowCalculator.kt
+++ b/src/main/kotlin/kr/co/vividnext/sodalive/chat/character/service/RankingWindowCalculator.kt
@@ -23,16 +23,24 @@ object RankingWindowCalculator {
     fun now(prefix: String = "popular-chat-character"): RankingWindow {
         val now = ZonedDateTime.now(ZONE)
         val todayBoundary = now.toLocalDate().atTime(BOUNDARY_HOUR, 0, 0).atZone(ZONE)
-        val (start, endExclusive, nextBoundary) = if (now.isBefore(todayBoundary)) {
-            val start = todayBoundary.minusDays(1)
-            Triple(start, todayBoundary, todayBoundary)
+
+        // 일일 순위는 "전날" 완료 구간을 보여주기 위해, 언제든 직전 경계까지만 집계한다.
+        // 예) 2025-09-14 20:00:00 직후에도 [2025-09-13 20:00, 2025-09-14 20:00) 윈도우를 사용
+        val lastBoundary = if (now.isBefore(todayBoundary)) {
+            // 아직 오늘 20:00 이전이면, 직전 경계는 어제 20:00
+            todayBoundary.minusDays(1)
         } else {
-            val next = todayBoundary.plusDays(1)
-            Triple(todayBoundary, next, next)
+            // 오늘 20:00을 지났거나 같으면, 직전 경계는 오늘 20:00
+            todayBoundary
         }
+
+        val start = lastBoundary.minusDays(1)
+        val endExclusive = lastBoundary
+
         val windowStart = start.toInstant()
-        val windowEnd = endExclusive.minusNanos(1).toInstant() // [start, end]
+        val windowEnd = endExclusive.minusSeconds(1).toInstant() // [start, end]
         val cacheKey = "$prefix:${windowStart.epochSecond}"
-        return RankingWindow(windowStart, windowEnd, nextBoundary.toInstant(), cacheKey)
+        // nextBoundary 필드는 기존 시그니처 유지를 위해 endExclusive(=lastBoundary)를 그대로 전달한다.
+        return RankingWindow(windowStart, windowEnd, endExclusive.toInstant(), cacheKey)
     }
 }