diff --git a/internal/handler/api_handler.go b/internal/handler/api_handler.go
index cec11bf..884632b 100644
--- a/internal/handler/api_handler.go
+++ b/internal/handler/api_handler.go
@@ -239,6 +239,7 @@ type CreateAssignmentInput struct {
 	Subject     string `json:"subject"`
 	Priority    string `json:"priority"`
 	DueDate     string `json:"due_date" binding:"required"`
+	SoftDueDate string `json:"soft_due_date"`
 
 	ReminderEnabled       bool   `json:"reminder_enabled"`
 	ReminderAt            string `json:"reminder_at"`
@@ -352,7 +353,17 @@ func (h *APIHandler) CreateAssignment(c *gin.Context) {
 		return
 	}
 
-	assignment, err := h.assignmentService.Create(userID, input.Title, input.Description, input.Subject, input.Priority, dueDate, input.ReminderEnabled, reminderAt, urgentReminder)
+	var softDueDate *time.Time
+	if input.SoftDueDate != "" {
+		parsedSoft, err := parseDateString(input.SoftDueDate)
+		if err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": "Invalid soft_due_date format"})
+			return
+		}
+		softDueDate = &parsedSoft
+	}
+
+	assignment, err := h.assignmentService.Create(userID, input.Title, input.Description, input.Subject, input.Priority, dueDate, softDueDate, input.ReminderEnabled, reminderAt, urgentReminder)
 	if err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to create assignment"})
 		return
@@ -367,6 +378,7 @@ type UpdateAssignmentInput struct {
 	Subject               string `json:"subject"`
 	Priority              string `json:"priority"`
 	DueDate               string `json:"due_date"`
+	SoftDueDate           string `json:"soft_due_date"`
 	ReminderEnabled       *bool  `json:"reminder_enabled"`
 	ReminderAt            string `json:"reminder_at"`
 	UrgentReminderEnabled *bool  `json:"urgent_reminder_enabled"`
@@ -448,7 +460,17 @@ func (h *APIHandler) UpdateAssignment(c *gin.Context) {
 		urgentReminderEnabled = *input.UrgentReminderEnabled
 	}
 
-	assignment, err := h.assignmentService.Update(userID, uint(id), title, description, subject, priority, dueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
+	softDueDate := existing.SoftDueDate
+	if input.SoftDueDate != "" {
+		parsedSoft, err := parseDateString(input.SoftDueDate)
+		if err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": "Invalid soft_due_date format"})
+			return
+		}
+		softDueDate = &parsedSoft
+	}
+
+	assignment, err := h.assignmentService.Update(userID, uint(id), title, description, subject, priority, dueDate, softDueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
 	if err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to update assignment"})
 		return
diff --git a/internal/handler/assignment_handler.go b/internal/handler/assignment_handler.go
index dd2ad4c..37c7ef3 100644
--- a/internal/handler/assignment_handler.go
+++ b/internal/handler/assignment_handler.go
@@ -111,14 +111,16 @@ func (h *AssignmentHandler) New(c *gin.Context) {
 	now := time.Now()
 	tomorrow := now.AddDate(0, 0, 1)
 	defaultDue := time.Date(tomorrow.Year(), tomorrow.Month(), tomorrow.Day(), 23, 59, 0, 0, now.Location())
+	defaultSoftDue := defaultDue.Add(-48 * time.Hour)
 
 	RenderHTML(c, http.StatusOK, "assignments/new.html", gin.H{
-		"title":          "課題登録",
-		"isAdmin":        role == "admin",
-		"userName":       name,
-		"currentWeekday": int(now.Weekday()),
-		"currentDay":     now.Day(),
-		"defaultDueDate": defaultDue.Format("2006-01-02T15:04"),
+		"title":              "課題登録",
+		"isAdmin":            role == "admin",
+		"userName":           name,
+		"currentWeekday":     int(now.Weekday()),
+		"currentDay":         now.Day(),
+		"defaultDueDate":     defaultDue.Format("2006-01-02T15:04"),
+		"defaultSoftDueDate": defaultSoftDue.Format("2006-01-02T15:04"),
 	})
 }
 
@@ -178,6 +180,16 @@ func (h *AssignmentHandler) Create(c *gin.Context) {
 		dueDate = dueDate.Add(23*time.Hour + 59*time.Minute)
 	}
 
+	var softDueDate *time.Time
+	if softDueDateStr := c.PostForm("soft_due_date"); softDueDateStr != "" {
+		if parsed, err := time.ParseInLocation("2006-01-02T15:04", softDueDateStr, time.Local); err == nil {
+			softDueDate = &parsed
+		} else if parsed, err := time.ParseInLocation("2006-01-02", softDueDateStr, time.Local); err == nil {
+			p := parsed.Add(23*time.Hour + 59*time.Minute)
+			softDueDate = &p
+		}
+	}
+
 	recurrenceType := c.PostForm("recurrence_type")
 	if recurrenceType != "" && recurrenceType != "none" {
 
@@ -265,7 +277,7 @@ func (h *AssignmentHandler) Create(c *gin.Context) {
 			return
 		}
 	} else {
-		assignment, err := h.assignmentService.Create(userID, title, description, subject, priority, dueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
+		assignment, err := h.assignmentService.Create(userID, title, description, subject, priority, dueDate, softDueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
 		if err != nil {
 			role, _ := c.Get(middleware.UserRoleKey)
 			name, _ := c.Get(middleware.UserNameKey)
@@ -352,7 +364,17 @@ func (h *AssignmentHandler) Update(c *gin.Context) {
 		dueDate = dueDate.Add(23*time.Hour + 59*time.Minute)
 	}
 
-	_, err = h.assignmentService.Update(userID, uint(id), title, description, subject, priority, dueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
+	var softDueDate *time.Time
+	if softDueDateStr := c.PostForm("soft_due_date"); softDueDateStr != "" {
+		if parsed, err := time.ParseInLocation("2006-01-02T15:04", softDueDateStr, time.Local); err == nil {
+			softDueDate = &parsed
+		} else if parsed, err := time.ParseInLocation("2006-01-02", softDueDateStr, time.Local); err == nil {
+			p := parsed.Add(23*time.Hour + 59*time.Minute)
+			softDueDate = &p
+		}
+	}
+
+	_, err = h.assignmentService.Update(userID, uint(id), title, description, subject, priority, dueDate, softDueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
 	if err != nil {
 		c.Redirect(http.StatusFound, "/assignments")
 		return
@@ -501,10 +523,9 @@ func (h *AssignmentHandler) ExportCSV(c *gin.Context) {
 	c.Header("Content-Disposition", "attachment; filename=\""+filename+"\"")
 
 	w := csv.NewWriter(c.Writer)
-	// UTF-8 BOM for Excel compatibility
 	c.Writer.Write([]byte("\xef\xbb\xbf"))
 
-	headers := []string{"ID", "タイトル", "科目", "説明", "重要度", "提出期限", "完了", "完了日時", "登録日時"}
+	headers := []string{"ID", "タイトル", "科目", "説明", "重要度", "提出期限", "自分の期限", "完了", "完了日時", "登録日時"}
 	w.Write(headers)
 
 	priorityLabel := map[string]string{"low": "低", "medium": "中", "high": "高"}
@@ -517,6 +538,10 @@ func (h *AssignmentHandler) ExportCSV(c *gin.Context) {
 		if a.CompletedAt != nil {
 			completedAt = a.CompletedAt.Format("2006/01/02 15:04")
 		}
+		softDueDateStr := ""
+		if a.SoftDueDate != nil {
+			softDueDateStr = a.SoftDueDate.Format("2006/01/02 15:04")
+		}
 		label := priorityLabel[a.Priority]
 		if label == "" {
 			label = a.Priority
@@ -528,6 +553,7 @@ func (h *AssignmentHandler) ExportCSV(c *gin.Context) {
 			a.Description,
 			label,
 			a.DueDate.Format("2006/01/02 15:04"),
+			softDueDateStr,
 			completed,
 			completedAt,
 			a.CreatedAt.Format("2006/01/02 15:04"),
diff --git a/internal/models/assignment.go b/internal/models/assignment.go
index 57f8d77..6600a79 100644
--- a/internal/models/assignment.go
+++ b/internal/models/assignment.go
@@ -14,6 +14,7 @@ type Assignment struct {
 	Subject                string     `json:"subject"`
 	Priority               string     `gorm:"not null;default:medium" json:"priority"`
 	DueDate                time.Time  `gorm:"not null" json:"due_date"`
+	SoftDueDate            *time.Time `json:"soft_due_date,omitempty"`
 	IsCompleted            bool       `gorm:"default:false" json:"is_completed"`
 	IsArchived             bool       `gorm:"default:false;index" json:"is_archived"`
 	CompletedAt            *time.Time `json:"completed_at,omitempty"`
@@ -23,7 +24,6 @@ type Assignment struct {
 	UrgentReminderEnabled  bool       `gorm:"default:true" json:"urgent_reminder_enabled"`
 	LastUrgentReminderSent *time.Time `json:"last_urgent_reminder_sent,omitempty"`
 
-	// Recurring assignment reference
 	RecurringAssignmentID *uint                `gorm:"index" json:"recurring_assignment_id,omitempty"`
 	RecurringAssignment   *RecurringAssignment `gorm:"foreignKey:RecurringAssignmentID" json:"-"`
 
@@ -34,6 +34,13 @@ type Assignment struct {
 	User *User `gorm:"foreignKey:UserID" json:"user,omitempty"`
 }
 
+func (a *Assignment) GetEffectiveSoftDueDate() time.Time {
+	if a.SoftDueDate != nil {
+		return *a.SoftDueDate
+	}
+	return a.DueDate.Add(-48 * time.Hour)
+}
+
 func (a *Assignment) IsOverdue() bool {
 	return !a.IsCompleted && time.Now().After(a.DueDate)
 }
diff --git a/internal/router/router.go b/internal/router/router.go
index dd8f249..78a47f4 100644
--- a/internal/router/router.go
+++ b/internal/router/router.go
@@ -25,11 +25,27 @@ func getFuncMap() template.FuncMap {
 		"formatDate": func(t time.Time) string {
 			return t.Format("2006/01/02")
 		},
-		"formatDateTime": func(t time.Time) string {
-			return t.Format("2006/01/02 15:04")
+		"formatDateTime": func(t interface{}) string {
+			switch v := t.(type) {
+			case time.Time:
+				return v.Format("2006/01/02 15:04")
+			case *time.Time:
+				if v != nil {
+					return v.Format("2006/01/02 15:04")
+				}
+			}
+			return ""
 		},
-		"formatDateInput": func(t time.Time) string {
-			return t.Format("2006-01-02T15:04")
+		"formatDateInput": func(t interface{}) string {
+			switch v := t.(type) {
+			case time.Time:
+				return v.Format("2006-01-02T15:04")
+			case *time.Time:
+				if v != nil {
+					return v.Format("2006-01-02T15:04")
+				}
+			}
+			return ""
 		},
 		"isOverdue": func(t time.Time, completed bool) bool {
 			return !completed && time.Now().After(t)
diff --git a/internal/service/assignment_service.go b/internal/service/assignment_service.go
index 7f86424..2042c95 100644
--- a/internal/service/assignment_service.go
+++ b/internal/service/assignment_service.go
@@ -31,7 +31,7 @@ func NewAssignmentService() *AssignmentService {
 	}
 }
 
-func (s *AssignmentService) Create(userID uint, title, description, subject, priority string, dueDate time.Time, reminderEnabled bool, reminderAt *time.Time, urgentReminderEnabled bool) (*models.Assignment, error) {
+func (s *AssignmentService) Create(userID uint, title, description, subject, priority string, dueDate time.Time, softDueDate *time.Time, reminderEnabled bool, reminderAt *time.Time, urgentReminderEnabled bool) (*models.Assignment, error) {
 	if priority == "" {
 		priority = "medium"
 	}
@@ -42,6 +42,7 @@ func (s *AssignmentService) Create(userID uint, title, description, subject, pri
 		Subject:               subject,
 		Priority:              priority,
 		DueDate:               dueDate,
+		SoftDueDate:           softDueDate,
 		IsCompleted:           false,
 		ReminderEnabled:       reminderEnabled,
 		ReminderAt:            reminderAt,
@@ -195,7 +196,7 @@ func (s *AssignmentService) SearchAssignments(userID uint, query, priority, filt
 	}, nil
 }
 
-func (s *AssignmentService) Update(userID, assignmentID uint, title, description, subject, priority string, dueDate time.Time, reminderEnabled bool, reminderAt *time.Time, urgentReminderEnabled bool) (*models.Assignment, error) {
+func (s *AssignmentService) Update(userID, assignmentID uint, title, description, subject, priority string, dueDate time.Time, softDueDate *time.Time, reminderEnabled bool, reminderAt *time.Time, urgentReminderEnabled bool) (*models.Assignment, error) {
 	assignment, err := s.GetByID(userID, assignmentID)
 	if err != nil {
 		return nil, err
@@ -206,6 +207,7 @@ func (s *AssignmentService) Update(userID, assignmentID uint, title, description
 	assignment.Subject = subject
 	assignment.Priority = priority
 	assignment.DueDate = dueDate
+	assignment.SoftDueDate = softDueDate
 	assignment.ReminderEnabled = reminderEnabled
 	assignment.ReminderAt = reminderAt
 	assignment.UrgentReminderEnabled = urgentReminderEnabled
diff --git a/internal/service/notification_service.go b/internal/service/notification_service.go
index 46599ea..e74d3d0 100644
--- a/internal/service/notification_service.go
+++ b/internal/service/notification_service.go
@@ -170,10 +170,11 @@ func (s *NotificationService) SendUrgentReminder(userID uint, assignment *models
 		return err
 	}
 
-	timeRemaining := time.Until(assignment.DueDate)
+	softDue := assignment.GetEffectiveSoftDueDate()
+	timeRemaining := time.Until(softDue)
 	var timeStr string
 	if timeRemaining < 0 {
-		timeStr = "期限切れ！"
+		timeStr = "自分の期限切れ！"
 	} else if timeRemaining < time.Hour {
 		timeStr = fmt.Sprintf("あと%d分", int(timeRemaining.Minutes()))
 	} else {
@@ -191,12 +192,13 @@ func (s *NotificationService) SendUrgentReminder(userID uint, assignment *models
 	}
 
 	message := fmt.Sprintf(
-		"%s 督促通知！\n\n【%s】\n科目: %s\n期限: %s (%s)\n\n完了したらアプリで完了ボタンを押してください！",
+		"%s 督促通知！\n\n【%s】\n科目: %s\n自分の期限: %s (%s)\nガチ期限: %s\n\n完了したらアプリで完了ボタンを押してください！",
 		priorityEmoji,
 		assignment.Title,
 		assignment.Subject,
-		assignment.DueDate.Format("2006/01/02 15:04"),
+		softDue.Format("2006/01/02 15:04"),
 		timeStr,
+		assignment.DueDate.Format("2006/01/02 15:04"),
 	)
 
 	var errors []string
@@ -268,9 +270,10 @@ func (s *NotificationService) ProcessUrgentReminders() {
 	}
 
 	for _, assignment := range assignments {
-		timeUntilDue := assignment.DueDate.Sub(now)
+		softDue := assignment.GetEffectiveSoftDueDate()
+		timeUntilSoftDue := softDue.Sub(now)
 
-		if timeUntilDue > urgentStartTime {
+		if timeUntilSoftDue > urgentStartTime {
 			continue
 		}
 
diff --git a/internal/service/recurring_assignment_service.go b/internal/service/recurring_assignment_service.go
index 4d9556e..6705280 100644
--- a/internal/service/recurring_assignment_service.go
+++ b/internal/service/recurring_assignment_service.go
@@ -244,26 +244,27 @@ func (s *RecurringAssignmentService) UpdateAssignmentWithBehavior(
 	assignment *models.Assignment,
 	title, description, subject, priority string,
 	dueDate time.Time,
+	softDueDate *time.Time,
 	reminderEnabled bool,
 	reminderAt *time.Time,
 	urgentReminderEnabled bool,
 	editBehavior string,
 ) error {
 	if assignment.RecurringAssignmentID == nil {
-		return s.updateSingleAssignment(assignment, title, description, subject, priority, dueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
+		return s.updateSingleAssignment(assignment, title, description, subject, priority, dueDate, softDueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
 	}
 
 	recurring, err := s.GetByID(userID, *assignment.RecurringAssignmentID)
 	if err != nil {
-		return s.updateSingleAssignment(assignment, title, description, subject, priority, dueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
+		return s.updateSingleAssignment(assignment, title, description, subject, priority, dueDate, softDueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
 	}
 
 	switch editBehavior {
 	case models.EditBehaviorThisOnly:
-		return s.updateSingleAssignment(assignment, title, description, subject, priority, dueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
+		return s.updateSingleAssignment(assignment, title, description, subject, priority, dueDate, softDueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
 
 	case models.EditBehaviorThisAndFuture:
-		if err := s.updateSingleAssignment(assignment, title, description, subject, priority, dueDate, reminderEnabled, reminderAt, urgentReminderEnabled); err != nil {
+		if err := s.updateSingleAssignment(assignment, title, description, subject, priority, dueDate, softDueDate, reminderEnabled, reminderAt, urgentReminderEnabled); err != nil {
 			return err
 		}
 		recurring.Title = title
@@ -288,7 +289,7 @@ func (s *RecurringAssignmentService) UpdateAssignmentWithBehavior(
 		return s.updateAllPendingAssignments(recurring.ID, title, description, subject, priority, urgentReminderEnabled)
 
 	default:
-		return s.updateSingleAssignment(assignment, title, description, subject, priority, dueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
+		return s.updateSingleAssignment(assignment, title, description, subject, priority, dueDate, softDueDate, reminderEnabled, reminderAt, urgentReminderEnabled)
 	}
 }
 
@@ -296,6 +297,7 @@ func (s *RecurringAssignmentService) updateSingleAssignment(
 	assignment *models.Assignment,
 	title, description, subject, priority string,
 	dueDate time.Time,
+	softDueDate *time.Time,
 	reminderEnabled bool,
 	reminderAt *time.Time,
 	urgentReminderEnabled bool,
@@ -305,6 +307,7 @@ func (s *RecurringAssignmentService) updateSingleAssignment(
 	assignment.Subject = subject
 	assignment.Priority = priority
 	assignment.DueDate = dueDate
+	assignment.SoftDueDate = softDueDate
 	assignment.ReminderEnabled = reminderEnabled
 	assignment.ReminderAt = reminderAt
 	assignment.UrgentReminderEnabled = urgentReminderEnabled
@@ -471,6 +474,8 @@ func (s *RecurringAssignmentService) generateAssignment(recurring *models.Recurr
 		reminderAt = &t
 	}
 
+	softDue := dueDate.Add(-48 * time.Hour)
+
 	assignment := &models.Assignment{
 		UserID:                recurring.UserID,
 		Title:                 recurring.Title,
@@ -478,6 +483,7 @@ func (s *RecurringAssignmentService) generateAssignment(recurring *models.Recurr
 		Subject:               recurring.Subject,
 		Priority:              recurring.Priority,
 		DueDate:               dueDate,
+		SoftDueDate:           &softDue,
 		ReminderEnabled:       recurring.ReminderEnabled,
 		ReminderAt:            reminderAt,
 		UrgentReminderEnabled: recurring.UrgentReminderEnabled,
diff --git a/web/templates/assignments/edit.html b/web/templates/assignments/edit.html
index 229bdb0..1a8aacf 100644
--- a/web/templates/assignments/edit.html
+++ b/web/templates/assignments/edit.html
@@ -28,9 +28,14 @@
                         </select>
                     </div>
                     <div class="mb-3">
-                        <label for="due_date" class="form-label">提出期限 <span class="text-danger" aria-hidden="true">*</span><span class="visually-hidden">（必須）</span></label>
+                        <label for="due_date" class="form-label">提出期限（ガチ期限） <span class="text-danger" aria-hidden="true">*</span><span class="visually-hidden">（必須）</span></label>
                         <input type="datetime-local" class="form-control" id="due_date" name="due_date" value="{{formatDateInput .assignment.DueDate}}" required>
                     </div>
+                    <div class="mb-3">
+                        <label for="soft_due_date" class="form-label">自分の期限 <span class="badge bg-secondary">任意</span></label>
+                        <input type="datetime-local" class="form-control" id="soft_due_date" name="soft_due_date" value="{{if .assignment.SoftDueDate}}{{formatDateInput .assignment.SoftDueDate}}{{end}}">
+                        <div class="form-text small text-muted">鬼督促はこの期限を基準に通知します。未指定の場合は提出期限の2日前になります。</div>
+                    </div>
                     <div class="mb-3">
                         <label for="description" class="form-label">説明</label>
                         <textarea class="form-control" id="description" name="description" rows="3">{{.assignment.Description}}</textarea>
diff --git a/web/templates/assignments/index.html b/web/templates/assignments/index.html
index 687e403..4b92a96 100644
--- a/web/templates/assignments/index.html
+++ b/web/templates/assignments/index.html
@@ -129,6 +129,7 @@
                         </td>
                         <td>
                             <div class="small fw-bold text-dark user-select-all">{{.DueDate.Format "2006/01/02 15:04"}}</div>
+                            {{if .SoftDueDate}}<div class="small text-info" title="自分の期限"><i class="bi bi-clock-history me-1" aria-hidden="true"></i>{{.SoftDueDate.Format "01/02 15:04"}}</div>{{end}}
                         </td>
                         <td class="countdown-col">
                             {{if not .IsCompleted}}
diff --git a/web/templates/assignments/new.html b/web/templates/assignments/new.html
index 3a0e5ac..1183545 100644
--- a/web/templates/assignments/new.html
+++ b/web/templates/assignments/new.html
@@ -28,9 +28,14 @@
                         </select>
                     </div>
                     <div class="mb-3">
-                        <label for="due_date" class="form-label">提出期限 <span class="text-danger" aria-hidden="true">*</span><span class="visually-hidden">（必須）</span></label>
+                        <label for="due_date" class="form-label">提出期限（ガチ期限） <span class="text-danger" aria-hidden="true">*</span><span class="visually-hidden">（必須）</span></label>
                         <input type="datetime-local" class="form-control" id="due_date" name="due_date" value="{{.defaultDueDate}}" required>
                     </div>
+                    <div class="mb-3">
+                        <label for="soft_due_date" class="form-label">自分の期限 <span class="badge bg-secondary">任意</span> <i class="bi bi-question-circle-fill text-muted" data-bs-toggle="tooltip" data-bs-placement="top" title="自分の期限とは、余裕を持って自分でこの期間までに提出するといった目標期限です。デフォルトでは2日前に設定されます。" aria-label="自分の期限の説明"></i></label>
+                        <input type="datetime-local" class="form-control" id="soft_due_date" name="soft_due_date" value="{{.defaultSoftDueDate}}">
+                        <div class="form-text small text-muted">鬼督促はこの期限を基準に通知します。</div>
+                    </div>
                     <div class="mb-3">
                         <label for="description" class="form-label">説明</label>
                         <textarea class="form-control" id="description" name="description" rows="3">{{.description}}</textarea>
@@ -156,6 +161,9 @@
     </div>
 </div>
 <script>
+    // Bootstrap tooltip初期化
+    document.querySelectorAll('[data-bs-toggle="tooltip"]').forEach(function(el) { new bootstrap.Tooltip(el); });
+
     function toggleReminderDate(checkbox) {
         document.getElementById('reminder_at_group').style.display = checkbox.checked ? 'block' : 'none';
     }
@@ -204,5 +212,25 @@
     document.getElementById('recurringSettings').addEventListener('show.bs.collapse', function () {
         updateLeadDaysMax();
     });
+
+    // Auto-sync soft_due_date when due_date changes
+    (function() {
+        var dueDateInput = document.getElementById('due_date');
+        var softDueDateInput = document.getElementById('soft_due_date');
+        var userEditedSoftDue = false;
+        softDueDateInput.addEventListener('input', function() { userEditedSoftDue = true; });
+        dueDateInput.addEventListener('change', function() {
+            if (userEditedSoftDue) return;
+            if (!dueDateInput.value) return;
+            var dueDate = new Date(dueDateInput.value);
+            dueDate.setDate(dueDate.getDate() - 2);
+            var y = dueDate.getFullYear();
+            var m = String(dueDate.getMonth() + 1).padStart(2, '0');
+            var d = String(dueDate.getDate()).padStart(2, '0');
+            var h = String(dueDate.getHours()).padStart(2, '0');
+            var min = String(dueDate.getMinutes()).padStart(2, '0');
+            softDueDateInput.value = y + '-' + m + '-' + d + 'T' + h + ':' + min;
+        });
+    })();
 </script>
 {{end}}
diff --git a/web/templates/pages/dashboard.html b/web/templates/pages/dashboard.html
index 83e1d2d..1d39b3c 100644
--- a/web/templates/pages/dashboard.html
+++ b/web/templates/pages/dashboard.html
@@ -115,6 +115,7 @@
                         {{if eq .Priority "high"}}<span class="badge bg-danger me-1">高<span class="visually-hidden">（重要度：高）</span></span>{{end}}
                         <strong>{{.Title}}</strong>
                         <br><small class="text-danger">{{formatDateTime .DueDate}}</small>
+                        {{if .SoftDueDate}}<br><small class="text-info"><i class="bi bi-clock-history" aria-hidden="true"></i> 自分の期限: {{formatDateTime .SoftDueDate}}</small>{{end}}
                     </div>
                     <form action="/assignments/{{.ID}}/toggle" method="POST">
                         <input type="hidden" name="_csrf" value="{{$.csrfToken}}">
@@ -140,6 +141,7 @@
                         {{if eq .Priority "high"}}<span class="badge bg-danger me-1">高<span class="visually-hidden">（重要度：高）</span></span>{{end}}
                         <strong>{{.Title}}</strong>
                         <br><small class="text-muted">{{formatDateTime .DueDate}}</small>
+                        {{if .SoftDueDate}}<br><small class="text-info"><i class="bi bi-clock-history" aria-hidden="true"></i> 自分の期限: {{formatDateTime .SoftDueDate}}</small>{{end}}
                     </div>
                     <form action="/assignments/{{.ID}}/toggle" method="POST">
                         <input type="hidden" name="_csrf" value="{{$.csrfToken}}">
@@ -165,6 +167,7 @@
                         {{if eq .Priority "high"}}<span class="badge bg-danger me-1">高<span class="visually-hidden">（重要度：高）</span></span>{{end}}
                         <strong>{{.Title}}</strong>
                         <br><small class="text-muted">{{formatDateTime .DueDate}}</small>
+                        {{if .SoftDueDate}}<br><small class="text-info"><i class="bi bi-clock-history" aria-hidden="true"></i> 自分の期限: {{formatDateTime .SoftDueDate}}</small>{{end}}
                     </div>
                     <form action="/assignments/{{.ID}}/toggle" method="POST">
                         <input type="hidden" name="_csrf" value="{{$.csrfToken}}">