diff --git a/Makefile b/Makefile
index 270dca7..1d0d3e9 100644
--- a/Makefile
+++ b/Makefile
@@ -19,6 +19,8 @@ day6:
 	php day6/main.php
 
 day7:
+	php day7/main.php
+
 day8:
 day9:
 day10:
diff --git a/day7/main.php b/day7/main.php
new file mode 100644
index 0000000..1f3acd3
--- /dev/null
+++ b/day7/main.php
@@ -0,0 +1,121 @@
+<?php
+// https://adventofcode.com/2017/day/7
+
+function puzzle1(string $input) : string
+{
+    $lines = explode(PHP_EOL, $input);
+    $children = [];
+    $names = [];
+
+    foreach ($lines as $line) {
+        // Split away master from children data
+        list($master, $child) = explode(' -> ', $line);
+
+        // Split number from name
+        list($masterName, $masterNumber) = explode(' ', $master);
+
+        // Map up children
+        if (!empty($child)) {
+            $children = array_merge($children, explode(', ', $child));
+        }
+
+        $names[] = $masterName;
+    }
+
+    // Flip children for faster lookup
+    $children = array_flip($children);
+
+    foreach ($names as $name) {
+        if (!isset($children[$name])) {
+            return $name;
+        }
+    }
+}
+
+function puzzle2(string $input) : int
+{
+    $lines = explode(PHP_EOL, $input);
+    $familyTree = [];
+    $names = [];
+    $grandparent = puzzle1($input);
+    $parentPoints = [];
+
+    foreach ($lines as $line) {
+        // Split away master from children data
+        list($master, $child) = explode(' -> ', $line);
+
+        // Split number from name and clean up the number
+        list($masterName, $masterNumber) = explode(' ', $master);
+        $masterNumber = str_replace(['(', ')'], '', $masterNumber);
+
+        // Map up children
+        if (!empty($child)) {
+            $familyTree[$masterName] = explode(', ', $child);
+        }
+
+        $names[$masterName] = $masterNumber;
+    }
+
+    function treePoints(array $familyTree, array $names, array &$wrongTrees, string $name) : int {
+        $points = 0;
+
+        if (isset($familyTree[$name])) {
+            $subtreePoints = [];
+
+            foreach ($familyTree[$name] as $subname) {
+                $subtreePoints[$subname] = $names[$subname] + treePoints($familyTree, $names, $wrongTrees, $subname);
+
+                $points += $names[$subname] + treePoints($familyTree, $names, $wrongTrees, $subname);
+            }
+
+            // If we have some error in this tree, put it into the list of wrongtrees
+            $copy = array_unique($subtreePoints);
+            if (count($copy) > 1) {
+                $wrongTrees[] = $subtreePoints;
+            }
+        }
+
+        return $points;
+    };
+
+    $wrongTrees = [];
+
+    // Extract the core family
+    foreach ($familyTree[$grandparent] as $name) {
+        $parentPoints[$name] = $names[$name] + treePoints($familyTree, $names, $wrongTrees, $name);
+    }
+
+    // Find which subtree that contains the error
+    $wrongTree = [];
+    foreach ($wrongTrees as $tree) {
+        foreach ($wrongTrees as $subtree) {
+            if (json_encode($tree) === json_encode($subtree)) {
+                $wrongTree = $tree;
+                break 2;
+            }
+        }
+    }
+
+    // Find a value that only exists once in the wrong tree
+    $errorNumber = 0;
+    $notErrorNumber = 0;
+    foreach (array_count_values($wrongTree) as $number => $count) {
+        if ($count === 1) {
+            $errorNumber = $number;
+        } else {
+            $notErrorNumber = $number;
+        }
+    }
+
+    // Find the broken name
+    $errorName = array_search($errorNumber, $wrongTree);
+
+    // calculate diff
+    $diff = $errorNumber - $notErrorNumber;
+
+    // Find original value of the errornus name
+    $errorNameOriginalValue = $names[$errorName];
+
+    // Calucalete correct value
+    return $errorNameOriginalValue - $diff;
+}