diff --git a/projects/aoc/src/year2021/Solutions2021.kiss b/projects/aoc/src/year2021/Solutions2021.kiss
index 2b60da11..14817f83 100644
--- a/projects/aoc/src/year2021/Solutions2021.kiss
+++ b/projects/aoc/src/year2021/Solutions2021.kiss
@@ -18,7 +18,9 @@
         (assert (= 4512 (winningScore "src/year2021/inputs/day4-example.txt")))
         (assert (= 46920 (winningScore "src/year2021/inputs/day4.txt"))))
     (dayTodo 5)
-    (dayTodo 6)
+    (day 6
+        (load "day6.kiss")
+        (print (countAfter "src/year2021/inputs/day6.txt" 80)))
     (dayTodo 7)
     (dayTodo 8)
     (dayTodo 9)
diff --git a/projects/aoc/src/year2021/day6.kiss b/projects/aoc/src/year2021/day6.kiss
new file mode 100644
index 00000000..3b15ff93
--- /dev/null
+++ b/projects/aoc/src/year2021/day6.kiss
@@ -0,0 +1,39 @@
+(defMacro dictInc [theMap key &builder b amount]
+    `(let [theMap ,theMap]
+        (unless (dictGet theMap ,key)
+            (dictSet theMap ,key 0))
+        (+= (dictGet theMap ,key) ,amount)))
+
+// Store the simulation state in a map of age => count.
+(function :Map<Int,Int> ageMap [:String file]
+    (let [:Array<Int> list (map (.split (first (Util.readLines file)) ",") Std.parseInt)
+            :Map<Int,Int> theMap (new Map)]
+        // special key -1 corresponds to total count
+        (dictSet theMap -1 list.length)
+        (doFor age (range 9)
+            (dictSet theMap age 0))
+        (doFor age list
+            (+= (dictGet theMap age) 1))
+        theMap))
+
+(function :Map<Int,Int> stepAgeMap [:Map<Int,Int> theMap]
+    // Lanternfish are guaranteed to be between 0-8 years old
+    (let [:Map<Int,Int> newMap (new Map)]
+        (dictSet newMap -1 (dictGet theMap -1))
+        (doFor age (range 9)
+            (let [count (dictGet theMap age)]
+                (case age
+                    // Lanternfish giving birth:
+                    (0
+                        (dictInc newMap 8 count)
+                        (dictInc newMap -1 count)
+                        (dictInc newMap 6 count))
+                    (otherwise
+                        (dictInc newMap (- age 1) count)))))
+        newMap))
+                    
+(function countAfter [file days]
+    (let [&mut ageMap (ageMap file)]
+        (doFor i (range days)
+            (set ageMap (stepAgeMap ageMap)))
+        (nth ageMap -1)))
\ No newline at end of file
diff --git a/projects/aoc/src/year2021/inputs/day6.txt b/projects/aoc/src/year2021/inputs/day6.txt
new file mode 100644
index 00000000..b800e1c3
--- /dev/null
+++ b/projects/aoc/src/year2021/inputs/day6.txt
@@ -0,0 +1 @@
+1,5,5,1,5,1,5,3,1,3,2,4,3,4,1,1,3,5,4,4,2,1,2,1,2,1,2,1,5,2,1,5,1,2,2,1,5,5,5,1,1,1,5,1,3,4,5,1,2,2,5,5,3,4,5,4,4,1,4,5,3,4,4,5,2,4,2,2,1,3,4,3,2,3,4,1,4,4,4,5,1,3,4,2,5,4,5,3,1,4,1,1,1,2,4,2,1,5,1,4,5,3,3,4,1,1,4,3,4,1,1,1,5,4,3,5,2,4,1,1,2,3,2,4,4,3,3,5,3,1,4,5,5,4,3,3,5,1,5,3,5,2,5,1,5,5,2,3,3,1,1,2,2,4,3,1,5,1,1,3,1,4,1,2,3,5,5,1,2,3,4,3,4,1,1,5,5,3,3,4,5,1,1,4,1,4,1,3,5,5,1,4,3,1,3,5,5,5,5,5,2,2,1,2,4,1,5,3,3,5,4,5,4,1,5,1,5,1,2,5,4,5,5,3,2,2,2,5,4,4,3,3,1,4,1,2,3,1,5,4,5,3,4,1,1,2,2,1,2,5,1,1,1,5,4,5,2,1,4,4,1,1,3,3,1,3,2,1,5,2,3,4,5,3,5,4,3,1,3,5,5,5,5,2,1,1,4,2,5,1,5,1,3,4,3,5,5,1,4,3