diff --git a/parts/4/blogApp/src/utils.js b/parts/4/blogApp/src/utils.js
index e2f9ea5..eadc74d 100644
--- a/parts/4/blogApp/src/utils.js
+++ b/parts/4/blogApp/src/utils.js
@@ -42,10 +42,30 @@ const favoritePost = (posts) => {
   return favoritePost;
 };
 
+const mostPosts = (posts) => {
+  if (!posts || posts.length === 0) {
+    return null;
+  }
+
+  const countMap = posts.reduce((acc, post) => {
+    acc[post.author] = (acc[post.author] || 0) + 1;
+    return acc;
+  }, {});
+
+  // Use Object.entries to find the top author
+  const [author, postsCount] = Object.entries(countMap).reduce(
+    (max, entry) => (entry[1] > max[1] ? entry : max),
+    ['', 0]
+  );
+
+  return { author, posts: postsCount };
+};
+
 module.exports = {
   reverse,
   average,
   listHelper,
   totalLikes,
   favoritePost,
+  mostPosts,
 };
diff --git a/parts/4/blogApp/tests/mostPosts.test.js b/parts/4/blogApp/tests/mostPosts.test.js
new file mode 100644
index 0000000..1b32452
--- /dev/null
+++ b/parts/4/blogApp/tests/mostPosts.test.js
@@ -0,0 +1,54 @@
+const { test, describe } = require("node:test");
+const assert = require("node:assert");
+const { mostPosts } = require("../src/utils");
+
+describe("most posts ", () => {
+  const posts = [
+    {
+      _id: "5a422aa71b54a676234d17f8",
+      title: "Go To Statement Considered Harmful",
+      author: "Edsger W. Dijkstra",
+      url: "https://homepages.cwi.nl/~storm/teaching/reader/Dijkstra68.pdf",
+      likes: 5,
+      __v: 0,
+    },
+    {
+      _id: "5a422aa71b54a676234d17f8",
+      title: "Go To Statement Considered Harmful",
+      author: "Edsger W. Dijkstra",
+      url: "https://homepages.cwi.nl/~storm/teaching/reader/Dijkstra68.pdf",
+      likes: 2,
+      __v: 0,
+    },
+    {
+      _id: "123",
+      title: "Lololo",
+      author: "John Doe",
+      url: "https://homepages.cwi.nl/~storm/teaching/reader/Dijkstra68.pdf",
+      likes: 1,
+      __v: 0,
+    },
+  ];
+
+  const emptyArray = [];
+
+  const gibberish = "asdaSd123asd";
+
+  test("finds top author  properly", () => {
+    assert.deepStrictEqual(mostPosts(posts), {
+      author: "Edsger W. Dijkstra",
+      posts: 2,
+    });
+  });
+
+  test("works fine with empty array", () => {
+    assert.strictEqual(mostPosts(emptyArray), null);
+  });
+
+  test("fails with gibberish input", () => {
+    const failedCall = () => {
+      mostPosts(gibberish);
+    };
+    assert.throws(failedCall, Error);
+  });
+});
diff --git a/parts/4/notes.md b/parts/4/notes.md
index 8263903..ccd63b9 100644
--- a/parts/4/notes.md
+++ b/parts/4/notes.md
@@ -4,3 +4,4 @@ Exercises:
 * [X] 4.3
 * [X] 4.4
 * [X] 4.5
+* [X] 4.6