<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Budget extends Model {
    public function tag() {
        return $this->belongsTo('App\Tag');
    }
}

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Budget extends Model {
    //
}

--- 
+++ 
@@ -5,5 +5,7 @@
 use Illuminate\Database\Eloquent\Model;
 
 class Budget extends Model {
-    //
+    public function tag() {
+        return $this->belongsTo('App\Tag');
+    }
 }
Add tag relationship to budget model
