diff --git a/2016/day12/main.go b/2016/day12/main.go
new file mode 100644
index 0000000..38ede8d
--- /dev/null
+++ b/2016/day12/main.go
@@ -0,0 +1,63 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	ans := assemblyComputer(util.ReadFile("./input.txt"), part)
+	fmt.Println("Output:", ans)
+}
+
+func assemblyComputer(input string, part int) int {
+	instructions := strings.Split(input, "\n")
+	registers := map[string]int{} // a b c d = 0
+	var instIndex int
+
+	if part == 2 {
+		registers["c"] = 1
+	}
+
+	for instIndex < len(instructions) {
+		parts := strings.Split(instructions[instIndex], " ")
+
+		switch parts[0] {
+		case "cpy":
+			valX, err := strconv.Atoi(parts[1])
+			if err != nil {
+				valX = registers[parts[1]]
+			}
+			registers[parts[2]] = valX
+			instIndex++
+		case "inc":
+			registers[parts[1]]++
+			instIndex++
+		case "dec":
+			registers[parts[1]]--
+			instIndex++
+		case "jnz":
+			valX, err := strconv.Atoi(parts[1])
+			if err != nil {
+				valX = registers[parts[1]]
+			}
+			if valX != 0 {
+				instIndex += cast.ToInt(parts[2])
+			} else {
+				instIndex++
+			}
+		}
+	}
+
+	return registers["a"]
+}
diff --git a/2016/day12/main_test.go b/2016/day12/main_test.go
new file mode 100644
index 0000000..3e321bd
--- /dev/null
+++ b/2016/day12/main_test.go
@@ -0,0 +1,26 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_assemblyComputer(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  int
+	}{
+		{"actual_part1", util.ReadFile("input.txt"), 1, 318077},
+		{"actual_part2", util.ReadFile("input.txt"), 2, 9227731},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := assemblyComputer(tt.input, tt.part); got != tt.want {
+				t.Errorf("assemblyComputer() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}