diff --git a/inputs/day06-example.txt b/inputs/day06-example.txt
new file mode 100644
index 0000000..55129f1
--- /dev/null
+++ b/inputs/day06-example.txt
@@ -0,0 +1 @@
+3,4,3,1,2
diff --git a/inputs/day06.txt b/inputs/day06.txt
new file mode 100644
index 0000000..8bed7ab
--- /dev/null
+++ b/inputs/day06.txt
@@ -0,0 +1 @@
+1,3,4,1,5,2,1,1,1,1,5,1,5,1,1,1,1,3,1,1,1,1,1,1,1,2,1,5,1,1,1,1,1,4,4,1,1,4,1,1,2,3,1,5,1,4,1,2,4,1,1,1,1,1,1,1,1,2,5,3,3,5,1,1,1,1,4,1,1,3,1,1,1,2,3,4,1,1,5,1,1,1,1,1,2,1,3,1,3,1,2,5,1,1,1,1,5,1,5,5,1,1,1,1,3,4,4,4,1,5,1,1,4,4,1,1,1,1,3,1,1,1,1,1,1,3,2,1,4,1,1,4,1,5,5,1,2,2,1,5,4,2,1,1,5,1,5,1,3,1,1,1,1,1,4,1,2,1,1,5,1,1,4,1,4,5,3,5,5,1,2,1,1,1,1,1,3,5,1,2,1,2,1,3,1,1,1,1,1,4,5,4,1,3,3,1,1,1,1,1,1,1,1,1,5,1,1,1,5,1,1,4,1,5,2,4,1,1,1,2,1,1,4,4,1,2,1,1,1,1,5,3,1,1,1,1,4,1,4,1,1,1,1,1,1,3,1,1,2,1,1,1,1,1,2,1,1,1,1,1,1,1,2,1,1,1,1,1,1,4,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,2,5,1,2,1,1,1,1,1,1,1,1,1
diff --git a/puzzles/day06.py b/puzzles/day06.py
new file mode 100644
index 0000000..85c9fe0
--- /dev/null
+++ b/puzzles/day06.py
@@ -0,0 +1,77 @@
+"""
+Advent of Code 2021 - day 06
+
+Run with:
+    python puzzles/day06.py inputs/day06.txt
+"""
+
+import pathlib
+import sys
+
+from collections import Counter
+from typing import List, Tuple
+
+
+class Reproduce:
+    times = None
+
+    def __init__(self, times: List[int]) -> None:
+        self.times = times
+
+    def start(self, days: int = 80) -> None:
+        counts = Counter(self.times)
+        for _ in range(days):
+            next_counts = Counter()  # Can't modify while iterating
+
+            for count_key, count in counts.items():
+                if count_key == 0:
+                    next_counts[8] += count  # Add the new fish
+                    next_counts[6] += count  # Move the parents back to 6 days
+                else:
+                    next_counts[count_key - 1] += count  # Move count to next day count
+
+            counts = next_counts
+        self.time_counts = counts
+
+    def count_fish(self) -> int:
+        return sum(self.time_counts.values())
+
+
+def part1(inputs: List[int]) -> int:
+    school = Reproduce(inputs)
+    school.start(days=80)
+    return school.count_fish()
+
+
+def part2(inputs: List[int]) -> int:
+    school = Reproduce(inputs)
+    school.start(days=256)
+    return school.count_fish()
+
+
+def parse(inputs: str) -> List[int]:
+    """Parse the input string"""
+    return [int(value) for value in inputs.split(",")]
+
+
+def solve(path: str) -> Tuple[int, int]:
+    """Solve the puzzle"""
+    puzzle_input = parse(pathlib.Path(path).read_text().strip())
+    part1_result = part1(puzzle_input)
+    part2_result = part2(puzzle_input)
+
+    return part1_result, part2_result
+
+
+def main() -> None:
+    for path in sys.argv[1:]:
+        print(f"Input File: {path}")
+
+        part1_result, part2_result = solve(path)
+
+        print(f"Part 1 Result: {part1_result}")
+        print(f"Part 2 Result: {part2_result}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/puzzles/test_day06.py b/puzzles/test_day06.py
new file mode 100644
index 0000000..e2a3250
--- /dev/null
+++ b/puzzles/test_day06.py
@@ -0,0 +1,32 @@
+import pathlib
+import pytest
+import day06 as aoc
+
+INPUTS_DIR = f"{pathlib.Path(__file__).parent.parent}/inputs"
+
+@pytest.fixture
+def example_data():
+    input_path = f"{INPUTS_DIR}/day06-example.txt"
+    return aoc.parse(pathlib.Path(input_path).read_text().strip())
+
+
+@pytest.fixture
+def day06_data():
+    input_path = f"{INPUTS_DIR}/day06.txt"
+    return aoc.parse(pathlib.Path(input_path).read_text().strip())
+
+
+def test_example1(example_data):
+    assert aoc.part1(example_data) == 5934
+
+
+def test_example2(example_data):
+    assert aoc.part2(example_data) == 26984457539
+
+
+def test_part1(day06_data):
+    assert aoc.part1(day06_data) == 386755
+
+
+def test_part2(day06_data):
+    assert aoc.part2(day06_data) == 1732731810807