diff --git a/06/input.txt b/06/input.txt
new file mode 100644
index 0000000..89b026d
--- /dev/null
+++ b/06/input.txt
@@ -0,0 +1 @@
+1,1,1,2,1,1,2,1,1,1,5,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,1,4,1,1,1,1,3,1,1,3,1,1,1,4,1,5,1,3,1,1,1,1,1,5,1,1,1,1,1,5,5,2,5,1,1,2,1,1,1,1,3,4,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,5,4,1,1,1,1,1,5,1,2,4,1,1,1,1,1,3,3,2,1,1,4,1,1,5,5,1,1,1,1,1,2,5,1,4,1,1,1,1,1,1,2,1,1,5,2,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,4,3,1,1,3,1,3,1,4,1,5,4,1,1,2,1,1,5,1,1,1,1,1,5,1,1,1,1,1,1,1,1,1,4,1,1,4,1,1,1,1,1,1,1,5,4,1,2,1,1,1,1,1,1,1,1,1,1,1,3,1,1,1,1,1,1,1,1,1,1,4,1,1,1,2,1,4,1,1,1,1,1,1,1,1,1,4,2,1,2,1,1,4,1,1,1,1,1,1,3,1,1,1,1,1,1,1,1,3,2,1,4,1,5,1,1,1,4,5,1,1,1,1,1,1,5,1,1,5,1,2,1,1,2,4,1,1,2,1,5,5,3
\ No newline at end of file
diff --git a/06/main.go b/06/main.go
new file mode 100644
index 0000000..629c143
--- /dev/null
+++ b/06/main.go
@@ -0,0 +1,64 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func main() {
+	inputBytes, _ := os.ReadFile("input.txt")
+	input := string(inputBytes)
+
+	log.Println("Puzzle 1:", puzzle1(input))
+	log.Println("Puzzle 2:", puzzle2(input))
+}
+
+func puzzle1(input string) int {
+	return do(input, 80)
+}
+
+func puzzle2(input string) int {
+	return do(input, 256)
+}
+
+func do(input string, days int) int {
+	var fish []int
+	total := 0
+	// Parse initial state
+	for _, s := range strings.Split(input, ",") {
+		f, _ := strconv.Atoi(s)
+		fish = append(fish, f)
+	}
+	// Run simulation for each fish
+	for _, f := range fish {
+		total += countDescendants(f, days)
+	}
+	return total
+}
+
+var cache = map[string]int{}
+
+func countDescendants(f int, days int) int {
+	if days == 0 || f-days >= 0 {
+		// Won't grow further
+		return 1
+	}
+	// Check cache
+	if c, ok := cache[fmt.Sprintf("%d:%d", f, days)]; ok {
+		return c
+	}
+	result := 0
+	if f == 0 {
+		// Add new fish
+		result = countDescendants(6, days-1) + countDescendants(8, days-1)
+	} else {
+		// Continue counting
+		result = countDescendants(f-1, days-1)
+	}
+	// Cache result
+	cache[fmt.Sprintf("%d:%d", f, days)] = result
+	return result
+}
diff --git a/06/main_test.go b/06/main_test.go
new file mode 100644
index 0000000..34cf1bd
--- /dev/null
+++ b/06/main_test.go
@@ -0,0 +1,16 @@
+package main
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test(t *testing.T) {
+	inputBytes, _ := os.ReadFile("test.txt")
+	input := string(inputBytes)
+
+	assert.Equal(t, 5934, puzzle1(input))
+	assert.Equal(t, 26984457539, puzzle2(input))
+}
diff --git a/06/test.txt b/06/test.txt
new file mode 100644
index 0000000..a7af2b1
--- /dev/null
+++ b/06/test.txt
@@ -0,0 +1 @@
+3,4,3,1,2
\ No newline at end of file