diff --git a/.aocrunner.json b/.aocrunner.json
index 1680657..a65854d 100644
--- a/.aocrunner.json
+++ b/.aocrunner.json
@@ -53,16 +53,16 @@
     },
     {
       "part1": {
-        "solved": false,
-        "result": null,
+        "solved": true,
+        "result": "11536",
         "attempts": [],
-        "time": null
+        "time": 20.05
       },
       "part2": {
-        "solved": false,
-        "result": null,
+        "solved": true,
+        "result": "1284",
         "attempts": [],
-        "time": null
+        "time": 55.8
       }
     },
     {
diff --git a/README.md b/README.md
index ab8b8cd..4ee999c 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@
 [![Day](https://badgen.net/badge/01/%E2%98%85%E2%98%85/green)](src/day01)
 [![Day](https://badgen.net/badge/02/%E2%98%85%E2%98%85/green)](src/day02)
 [![Day](https://badgen.net/badge/03/%E2%98%85%E2%98%85/green)](src/day03)
-![Day](https://badgen.net/badge/04/%E2%98%86%E2%98%86/gray)
+[![Day](https://badgen.net/badge/04/%E2%98%85%E2%98%85/green)](src/day04)
 ![Day](https://badgen.net/badge/05/%E2%98%86%E2%98%86/gray)
 ![Day](https://badgen.net/badge/06/%E2%98%86%E2%98%86/gray)
 ![Day](https://badgen.net/badge/07/%E2%98%86%E2%98%86/gray)
@@ -90,9 +90,9 @@ Both parts: 7.29ms
 
 ```
 Day 04
-Time part 1: -
-Time part 2: -
-Both parts: -
+Time part 1: 20.05ms
+Time part 2: 55.8ms
+Both parts: 75.85ms
 ```
 
 ```
@@ -243,8 +243,8 @@ Both parts: -
 ```
 
 ```
-Total stars: 6/50
-Total time: 13.15ms
+Total stars: 8/50
+Total time: 89ms
 ```
 
 <!--/RESULTS-->
diff --git a/src/day04/README.md b/src/day04/README.md
new file mode 100644
index 0000000..a0638c1
--- /dev/null
+++ b/src/day04/README.md
@@ -0,0 +1,9 @@
+# 🎄 Advent of Code 2021 - day 4 🎄
+
+## Info
+
+Task description: [link](https://adventofcode.com/2021/day/4)
+
+## Notes
+
+...
\ No newline at end of file
diff --git a/src/day04/index.js b/src/day04/index.js
new file mode 100644
index 0000000..954d13b
--- /dev/null
+++ b/src/day04/index.js
@@ -0,0 +1,143 @@
+import run from "aocrunner"
+import { transpose } from "../utils/index.js"
+
+function check(board) {
+  const board2 = transpose(board)
+  for (let i = 0; i < 5; i++) {
+    if (
+      board[i].every((x) => x === null) ||
+      board2[i].every((x) => x === null)
+    ) {
+      return true
+    }
+  }
+  return false
+}
+
+const parseInput = (rawInput) => {
+  const lines = rawInput.trim().split`\n`
+  const calls = lines.shift().split`,`.map(Number)
+  const boards = []
+  while (lines.length > 0) {
+    const nextBoard = []
+    lines.shift() //blank line
+    for (let i = 0; i < 5; i++) {
+      nextBoard[i] = lines.shift().trim().split(/\s+/).map(Number)
+    }
+    boards.push(nextBoard)
+  }
+  return { calls, boards }
+}
+
+const part1 = (rawInput) => {
+  const { calls, boards } = parseInput(rawInput)
+  const marked = []
+  let winningBoard, lastCall
+  outer: for (const call of calls) {
+    lastCall = call
+    for (const board of boards) {
+      for (const row of board) {
+        for (let i = 0; i < 5; i++) {
+          if (row[i] === call) {
+            row[i] = null
+            if (check(board)) {
+              winningBoard = board
+              break outer
+            }
+          }
+        }
+      }
+    }
+  }
+
+  const sum = winningBoard.reduce(
+    (acc, row) => acc + row.reduce((acc2, cell) => acc2 + cell, 0),
+    0,
+  )
+  return sum * lastCall
+}
+
+const part2 = (rawInput) => {
+  const { calls, boards } = parseInput(rawInput)
+  const marked = []
+  let winningSum, lastCall
+  for (const call of calls) {
+    for (const board of boards) {
+      for (const row of board) {
+        for (let i = 0; i < 5; i++) {
+          if (row[i] === call) {
+            row[i] = null
+            if (check(board)) {
+              lastCall = call
+              winningSum = board.reduce(
+                (acc, row) => acc + row.reduce((acc2, cell) => acc2 + cell, 0),
+                0,
+              )
+              board.splice(0, 5)
+            }
+          }
+        }
+      }
+    }
+  }
+
+  return winningSum * lastCall
+}
+
+run({
+  part1: {
+    tests: [
+      {
+        input: `7,4,9,5,11,17,23,2,0,14,21,24,10,16,13,6,15,25,12,22,18,20,8,19,3,26,1
+
+22 13 17 11  0
+ 8  2 23  4 24
+21  9 14 16  7
+ 6 10  3 18  5
+ 1 12 20 15 19
+
+ 3 15  0  2 22
+ 9 18 13 17  5
+19  8  7 25 23
+20 11 10 24  4
+14 21 16 12  6
+
+14 21 17 24  4
+10 16 15  9 19
+18  8 23 26 20
+22 11 13  6  5
+ 2  0 12  3  7`,
+        expected: 4512,
+      },
+    ],
+    solution: part1,
+  },
+  part2: {
+    tests: [
+      {
+        input: `7,4,9,5,11,17,23,2,0,14,21,24,10,16,13,6,15,25,12,22,18,20,8,19,3,26,1
+
+22 13 17 11  0
+ 8  2 23  4 24
+21  9 14 16  7
+ 6 10  3 18  5
+ 1 12 20 15 19
+
+ 3 15  0  2 22
+ 9 18 13 17  5
+19  8  7 25 23
+20 11 10 24  4
+14 21 16 12  6
+
+14 21 17 24  4
+10 16 15  9 19
+18  8 23 26 20
+22 11 13  6  5
+ 2  0 12  3  7`,
+        expected: 1924,
+      },
+    ],
+    solution: part2,
+  },
+  trimTestInputs: true,
+})
diff --git a/src/utils/index.js b/src/utils/index.js
index 70b969c..c847683 100644
--- a/src/utils/index.js
+++ b/src/utils/index.js
@@ -22,3 +22,6 @@
  *     import myLib from '../utils/myLib'
  *     import { myUtil } from '../utils'
  */
+export function transpose(m) {
+  return m[0].map((x, i) => m.map((x) => x[i]))
+}