diff --git a/2021/src/main/kotlin/Day06.kt b/2021/src/main/kotlin/Day06.kt
new file mode 100644
index 0000000..c0673bd
--- /dev/null
+++ b/2021/src/main/kotlin/Day06.kt
@@ -0,0 +1,27 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.BaseDay
+import be.vandewalleh.aoc.utils.input.Day
+
+@Day
+class Day06 : BaseDay() {
+    override fun part1() = run(80)
+    override fun part2() = run(256)
+
+    private fun run(days: Int): Long {
+        var fish = LongArray(9)
+        input.csv.ints.forEach { fish[it] = fish[it] + 1 }
+
+        var newFish: LongArray
+        for (day in 1..days) {
+            newFish = LongArray(9)
+            for (timer in 8 downTo 1) {
+                newFish[timer - 1] = fish[timer]
+            }
+            newFish[8] = fish[0]
+            newFish[6] = fish[0] + newFish[6]
+            fish = newFish
+        }
+        return fish.sum()
+    }
+}
diff --git a/2021/src/main/resources/day06.txt b/2021/src/main/resources/day06.txt
new file mode 100644
index 0000000..445de95
--- /dev/null
+++ b/2021/src/main/resources/day06.txt
@@ -0,0 +1 @@
+1,1,3,1,3,2,1,3,1,1,3,1,1,2,1,3,1,1,3,5,1,1,1,3,1,2,1,1,1,1,4,4,1,2,1,2,1,1,1,5,3,2,1,5,2,5,3,3,2,2,5,4,1,1,4,4,1,1,1,1,1,1,5,1,2,4,3,2,2,2,2,1,4,1,1,5,1,3,4,4,1,1,3,3,5,5,3,1,3,3,3,1,4,2,2,1,3,4,1,4,3,3,2,3,1,1,1,5,3,1,4,2,2,3,1,3,1,2,3,3,1,4,2,2,4,1,3,1,1,1,1,1,2,1,3,3,1,2,1,1,3,4,1,1,1,1,5,1,1,5,1,1,1,4,1,5,3,1,1,3,2,1,1,3,1,1,1,5,4,3,3,5,1,3,4,3,3,1,4,4,1,2,1,1,2,1,1,1,2,1,1,1,1,1,5,1,1,2,1,5,2,1,1,2,3,2,3,1,3,1,1,1,5,1,1,2,1,1,1,1,3,4,5,3,1,4,1,1,4,1,4,1,1,1,4,5,1,1,1,4,1,3,2,2,1,1,2,3,1,4,3,5,1,5,1,1,4,5,5,1,1,3,3,1,1,1,1,5,5,3,3,2,4,1,1,1,1,1,5,1,1,2,5,5,4,2,4,4,1,1,3,3,1,5,1,1,1,1,1,1
diff --git a/2021/src/test/kotlin/Day06Test.kt b/2021/src/test/kotlin/Day06Test.kt
new file mode 100644
index 0000000..d78ab69
--- /dev/null
+++ b/2021/src/test/kotlin/Day06Test.kt
@@ -0,0 +1,13 @@
+package be.vandewalleh.aoc.days
+
+class Day06Test : BaseDayTest(6) {
+    override val example = """
+        3,4,3,1,2
+    """.trimIndent()
+
+    override val part1Example = 5934L
+    override val part1Answer = 373378L
+
+    override val part2Example = 26984457539
+    override val part2Answer = 1682576647495
+}