diff --git a/app.py b/app.py
index 22aeedd..123178a 100644
--- a/app.py
+++ b/app.py
@@ -5,6 +5,7 @@ from flask import Flask, render_template, redirect, url_for, request
 from flask_login import login_required, LoginManager, login_user, logout_user, current_user
 
 from models.Habit import Habit
+from models.HabitTrackings import HabitTrackings
 from models.User import User
 from utils import anonymous_required
 
@@ -223,8 +224,33 @@ def habit_create():
 @app.route('/check', methods=['POST'])
 @login_required
 def check_habit():
-    habit = request.get_json()["habitId"]
-    return {}
+    habit_id = request.get_json()["habitId"]
+
+    habit = Habit.get(habit_id)
+
+    if habit is None:
+        return {"error": "Habit not found"}
+
+    # Check if habit belongs to user
+    if habit.user_id != current_user.id:
+        return {"error": "Habit does not belong to user"}
+
+    trackings = habit.get_habitTrackings()
+
+    # Check if habit has been tracked today
+    unchecked = False
+    for tracking in trackings:
+        if tracking.created_at.date() == datetime.date.today():
+            tracking.delete()
+            unchecked = True
+
+    if not unchecked:
+        HabitTrackings.create(habit_id, 1)
+
+    return {
+        "habitId": habit_id,
+        "unchecked": unchecked,
+    }
 
 
 # Run the application