diff --git a/2021/day11/day11.bqn b/2021/day11/day11.bqn
new file mode 100644
index 0000000..9acff2c
--- /dev/null
+++ b/2021/day11/day11.bqn
@@ -0,0 +1,13 @@
+in←'0'-˜>•FLines"input"
+
+fs←⟨«,»,«˘,»˘,»∘(»˘),«∘(«˘),«∘(»˘),«˘∘»⟩
+Flash←{𝕊flashed‿m:
+  flashed+↩9<m
+  ⟨flashed,(¬flashed)×m++´fs{𝕎𝕩}¨<9<m⟩
+}
+Step←{𝕊f‿m:
+  Flash•_while_{∨´⥊9<1⊑𝕩} ⟨(≢f)⥊0,1+m⟩
+}
+•Show +´⥊+´⊑¨Step⍟(1+↕100)⟨(≢in)⥊0,in⟩
+
+•Show ⊑/∧´∘⥊¨⊑¨Step⍟(↕300)⟨(≢in)⥊0,in⟩
diff --git a/2021/day11/input b/2021/day11/input
new file mode 100644
index 0000000..601f999
--- /dev/null
+++ b/2021/day11/input
@@ -0,0 +1,10 @@
+8261344656
+7773351175
+7527856852
+1763614673
+8674556743
+6853382153
+4135852388
+2846715522
+7477425863
+4723888888
diff --git a/2021/day11/smalltest b/2021/day11/smalltest
new file mode 100644
index 0000000..ae21dd2
--- /dev/null
+++ b/2021/day11/smalltest
@@ -0,0 +1,5 @@
+11111
+19991
+19191
+19991
+11111
diff --git a/2021/day11/test b/2021/day11/test
new file mode 100644
index 0000000..03743f6
--- /dev/null
+++ b/2021/day11/test
@@ -0,0 +1,10 @@
+5483143223
+2745854711
+5264556173
+6141336146
+6357385478
+4167524645
+2176841721
+6882881134
+4846848554
+5283751526