diff --git a/2018/day12.py b/2018/day12.py
new file mode 100644
index 0000000..158d31d
--- /dev/null
+++ b/2018/day12.py
@@ -0,0 +1,34 @@
+import fileinput
+
+
+INITIAL = None
+RULES = {}
+GENS = 200  # 200 generations is safe for the automata to converge
+TARGET_GEN = 50000000000
+
+for i, line in enumerate(fileinput.input()):
+    if i == 0:
+        INITIAL = line.split()[-1]
+    elif i >= 2:
+        a, _, b = line.split()
+        RULES[a] = b
+
+
+state = ['.'] * GENS + list(INITIAL) + ['.'] * GENS
+pot_sums = []
+
+for it in range(GENS):
+    amt = sum(i - GENS for i, p in enumerate(state) if p == '#')
+    pot_sums.append(amt)
+
+    next_state = ['.'] * len(state)
+    for i in range(len(state) - 2):
+        next_state[i + 2] = RULES.get(''.join(state[i:i+5]), '.')
+
+    state = next_state
+
+print "Sum of plants after 20 generations:", pot_sums[20]
+
+growth_per_gen = pot_sums[-1] - pot_sums[-2]
+remaining_gens = TARGET_GEN - GENS + 1
+print "Sum after 50000000000 generations:", growth_per_gen * remaining_gens + pot_sums[-1]
diff --git a/2018/inputs/12.txt b/2018/inputs/12.txt
new file mode 100644
index 0000000..da50317
--- /dev/null
+++ b/2018/inputs/12.txt
@@ -0,0 +1,34 @@
+initial state: #...####.##..####..#.##....##...###.##.#..######..#..#..###..##.#.###.#####.##.#.#.#.##....#..#..#..
+
+...## => .
+...#. => #
+....# => .
+###.# => #
+..... => .
+..#.. => .
+#.#.# => .
+#..#. => .
+#...# => .
+##... => .
+.#.#. => #
+.#..# => .
+.###. => .
+#..## => #
+..#.# => #
+.#### => #
+##..# => #
+##.#. => #
+.#... => #
+#.#.. => .
+##### => .
+###.. => #
+.##.# => .
+#.##. => .
+..### => .
+.#.## => #
+..##. => #
+#.### => .
+.##.. => #
+##.## => .
+#.... => .
+####. => #
diff --git a/2018/outputs/12.txt b/2018/outputs/12.txt
new file mode 100644
index 0000000..1c3e8d5
--- /dev/null
+++ b/2018/outputs/12.txt
@@ -0,0 +1,2 @@
+3410
+4000000001480