diff --git a/backend/src/routes/schedules/index.js b/backend/src/routes/schedules/index.js
index ece2f73..fc5eb4e 100644
--- a/backend/src/routes/schedules/index.js
+++ b/backend/src/routes/schedules/index.js
@@ -4,8 +4,13 @@
  */
 import suggestionsRoutes from './suggestions.js';
 import { searchSchedules, syncAllSchedules } from '../../services/meilisearch/index.js';
-import config, { CATEGORY_IDS } from '../../config/index.js';
-import { getMonthlySchedules, getUpcomingSchedules } from '../../services/schedule.js';
+import { CATEGORY_IDS } from '../../config/index.js';
+import {
+  getCategories,
+  getScheduleDetail,
+  getMonthlySchedules,
+  getUpcomingSchedules,
+} from '../../services/schedule.js';
 import {
   errorResponse,
   scheduleSearchQuery,
@@ -34,10 +39,7 @@ export default async function schedulesRoutes(fastify) {
     },
   }, async (request, reply) => {
     try {
-      const [categories] = await db.query(
-        'SELECT id, name, color, sort_order FROM schedule_categories ORDER BY sort_order ASC, id ASC'
-      );
-      return categories;
+      return await getCategories(db);
     } catch (err) {
       fastify.log.error(err);
       return reply.code(500).send({ error: '카테고리 목록 조회 실패' });
@@ -132,89 +134,16 @@ export default async function schedulesRoutes(fastify) {
     },
   }, async (request, reply) => {
     try {
-      const { id } = request.params;
+      const result = await getScheduleDetail(
+        db,
+        request.params.id,
+        (username) => fastify.xBot.getProfile(username)
+      );
 
-      const [schedules] = await db.query(`
-        SELECT
-          s.*,
-          c.name as category_name,
-          c.color as category_color,
-          sy.channel_name as youtube_channel,
-          sy.video_id as youtube_video_id,
-          sy.video_type as youtube_video_type,
-          sx.post_id as x_post_id,
-          sx.content as x_content,
-          sx.image_urls as x_image_urls
-        FROM schedules s
-        LEFT JOIN schedule_categories c ON s.category_id = c.id
-        LEFT JOIN schedule_youtube sy ON s.id = sy.schedule_id
-        LEFT JOIN schedule_x sx ON s.id = sx.schedule_id
-        WHERE s.id = ?
-      `, [id]);
-
-      if (schedules.length === 0) {
+      if (!result) {
         return reply.code(404).send({ error: '일정을 찾을 수 없습니다.' });
       }
 
-      const s = schedules[0];
-
-      // 멤버 정보 조회
-      const [members] = await db.query(`
-        SELECT m.id, m.name
-        FROM schedule_members sm
-        JOIN members m ON sm.member_id = m.id
-        WHERE sm.schedule_id = ?
-        ORDER BY m.id
-      `, [id]);
-
-      // datetime 생성 (date + time)
-      const dateStr = s.date instanceof Date ? s.date.toISOString().split('T')[0] : s.date?.split('T')[0];
-      const timeStr = s.time ? s.time.slice(0, 5) : null;
-      const datetime = timeStr ? `${dateStr} ${timeStr}` : dateStr;
-
-      // 공통 필드
-      const result = {
-        id: s.id,
-        title: s.title,
-        datetime,
-        category: {
-          id: s.category_id,
-          name: s.category_name,
-          color: s.category_color,
-        },
-        members,
-        createdAt: s.created_at,
-        updatedAt: s.updated_at,
-      };
-
-      // 카테고리별 추가 필드
-      if (s.category_id === CATEGORY_IDS.YOUTUBE && s.youtube_video_id) {
-        // YouTube
-        result.videoId = s.youtube_video_id;
-        result.videoType = s.youtube_video_type;
-        result.channelName = s.youtube_channel;
-        result.videoUrl = s.youtube_video_type === 'shorts'
-          ? `https://www.youtube.com/shorts/${s.youtube_video_id}`
-          : `https://www.youtube.com/watch?v=${s.youtube_video_id}`;
-      } else if (s.category_id === CATEGORY_IDS.X && s.x_post_id) {
-        // X (Twitter)
-        const username = config.x.defaultUsername;
-        result.postId = s.x_post_id;
-        result.content = s.x_content || null;
-        result.imageUrls = s.x_image_urls ? JSON.parse(s.x_image_urls) : [];
-        result.postUrl = `https://x.com/${username}/status/${s.x_post_id}`;
-
-        // 프로필 정보 (Redis 캐시 → DB)
-        const profile = await fastify.xBot.getProfile(username);
-        if (profile) {
-          result.profile = {
-            username: profile.username,
-            displayName: profile.displayName,
-            avatarUrl: profile.avatarUrl,
-          };
-        }
-      }
-
       return result;
     } catch (err) {
       fastify.log.error(err);
diff --git a/backend/src/services/schedule.js b/backend/src/services/schedule.js
index c5de8db..637f3ee 100644
--- a/backend/src/services/schedule.js
+++ b/backend/src/services/schedule.js
@@ -4,6 +4,112 @@
  */
 import config, { CATEGORY_IDS } from '../config/index.js';
 
+/**
+ * 카테고리 목록 조회
+ * @param {object} db - 데이터베이스 연결
+ * @returns {array} 카테고리 목록
+ */
+export async function getCategories(db) {
+  const [categories] = await db.query(
+    'SELECT id, name, color, sort_order FROM schedule_categories ORDER BY sort_order ASC, id ASC'
+  );
+  return categories;
+}
+
+/**
+ * 일정 상세 조회
+ * @param {object} db - 데이터베이스 연결
+ * @param {number} id - 일정 ID
+ * @param {Function} getXProfile - X 프로필 조회 함수 (선택적)
+ * @returns {object|null} 일정 상세 또는 null
+ */
+export async function getScheduleDetail(db, id, getXProfile = null) {
+  const [schedules] = await db.query(`
+    SELECT
+      s.*,
+      c.name as category_name,
+      c.color as category_color,
+      sy.channel_name as youtube_channel,
+      sy.video_id as youtube_video_id,
+      sy.video_type as youtube_video_type,
+      sx.post_id as x_post_id,
+      sx.content as x_content,
+      sx.image_urls as x_image_urls
+    FROM schedules s
+    LEFT JOIN schedule_categories c ON s.category_id = c.id
+    LEFT JOIN schedule_youtube sy ON s.id = sy.schedule_id
+    LEFT JOIN schedule_x sx ON s.id = sx.schedule_id
+    WHERE s.id = ?
+  `, [id]);
+
+  if (schedules.length === 0) {
+    return null;
+  }
+
+  const s = schedules[0];
+
+  // 멤버 정보 조회
+  const [members] = await db.query(`
+    SELECT m.id, m.name
+    FROM schedule_members sm
+    JOIN members m ON sm.member_id = m.id
+    WHERE sm.schedule_id = ?
+    ORDER BY m.id
+  `, [id]);
+
+  // datetime 생성 (date + time)
+  const dateStr = s.date instanceof Date ? s.date.toISOString().split('T')[0] : s.date?.split('T')[0];
+  const timeStr = s.time ? s.time.slice(0, 5) : null;
+  const datetime = timeStr ? `${dateStr} ${timeStr}` : dateStr;
+
+  // 공통 필드
+  const result = {
+    id: s.id,
+    title: s.title,
+    datetime,
+    category: {
+      id: s.category_id,
+      name: s.category_name,
+      color: s.category_color,
+    },
+    members,
+    createdAt: s.created_at,
+    updatedAt: s.updated_at,
+  };
+
+  // 카테고리별 추가 필드
+  if (s.category_id === CATEGORY_IDS.YOUTUBE && s.youtube_video_id) {
+    // YouTube
+    result.videoId = s.youtube_video_id;
+    result.videoType = s.youtube_video_type;
+    result.channelName = s.youtube_channel;
+    result.videoUrl = s.youtube_video_type === 'shorts'
+      ? `https://www.youtube.com/shorts/${s.youtube_video_id}`
+      : `https://www.youtube.com/watch?v=${s.youtube_video_id}`;
+  } else if (s.category_id === CATEGORY_IDS.X && s.x_post_id) {
+    // X (Twitter)
+    const username = config.x.defaultUsername;
+    result.postId = s.x_post_id;
+    result.content = s.x_content || null;
+    result.imageUrls = s.x_image_urls ? JSON.parse(s.x_image_urls) : [];
+    result.postUrl = `https://x.com/${username}/status/${s.x_post_id}`;
+
+    // 프로필 정보 (선택적)
+    if (getXProfile) {
+      const profile = await getXProfile(username);
+      if (profile) {
+        result.profile = {
+          username: profile.username,
+          displayName: profile.displayName,
+          avatarUrl: profile.avatarUrl,
+        };
+      }
+    }
+  }
+
+  return result;
+}
+
 /**
  * 월별 일정 조회 (생일 포함)
  * @param {object} db - 데이터베이스 연결
diff --git a/docs/refactoring.md b/docs/refactoring.md
index 9851336..4a980c5 100644
--- a/docs/refactoring.md
+++ b/docs/refactoring.md
@@ -211,13 +211,13 @@
 
 ---
 
-### 20단계: 서비스 레이어 확대 🔄 진행 예정
-- [ ] schedules 라우트의 DB 쿼리를 서비스로 분리
-- [ ] 일관된 서비스 패턴 적용
+### 20단계: 서비스 레이어 확대 ✅ 완료
+- [x] schedules 라우트의 DB 쿼리를 서비스로 분리
+- [x] 일관된 서비스 패턴 적용
 
-**대상 파일:**
-- `src/services/schedule.js` - 함수 추가
-- `src/routes/schedules/index.js` - 서비스 호출로 변경
+**수정된 파일:**
+- `src/services/schedule.js` - getCategories, getScheduleDetail 함수 추가
+- `src/routes/schedules/index.js` - 서비스 호출로 변경 (약 70줄 감소)
 
 ---
 
@@ -253,7 +253,7 @@
 | 17단계 | 중복 코드 제거 (멤버 조회) | ✅ 완료 |
 | 18단계 | 이미지 처리 최적화 | ✅ 완료 |
 | 19단계 | Redis 캐시 확대 | ✅ 완료 |
-| 20단계 | 서비스 레이어 확대 | 🔄 진행 예정 |
+| 20단계 | 서비스 레이어 확대 | ✅ 완료 |
 | 21단계 | 검색 페이징 최적화 | 🔄 진행 예정 |
 
 ---