There's a giant mix brewing between "old" code, bad code and not implemented exceptions. I suspect the next change will be to cut out all old stuff, throw a lot of NotImplementedExceptions and get going.

app/lib/FireflyIII/Shared/Toolkit/Filter.php

@@ -24,7 +24,7 @@ class Filter
      *
      * @return string
      */
-    protected function setSessionRangeValue()
+    public function setSessionRangeValue()
     {
         if (!is_null(\Session::get('range'))) {
             $range = \Session::get('range');
@@ -221,7 +221,7 @@ class Filter
      * @return Carbon
      * @throws FireflyException
      */
-    protected function previous($range, Carbon $date)
+    public function previous($range, Carbon $date)
     {
         switch ($range) {
             default:
@@ -262,7 +262,7 @@ class Filter
      * @return Carbon
      * @throws FireflyException
      */
-    protected function next($range, Carbon $date)
+    public function next($range, Carbon $date)
     {
         switch ($range) {
             case '1D':

app/lib/FireflyIII/Shared/Toolkit/Navigation.php

@@ -0,0 +1,64 @@
+<?php
+
+namespace FireflyIII\Shared\Toolkit;
+
+/**
+ * Class Navigation
+ *
+ * @package FireflyIII\Shared\Toolkit
+ */
+class Navigation
+{
+    /**
+     * @return bool
+     * @throws \Firefly\Exception\FireflyException
+     */
+    public function next()
+    {
+        /*
+         * Get the start date and the range from the session
+         */
+
+        $filter = new Filter;
+
+        $range = $filter->setSessionRangeValue();
+        $start = \Session::get('start');
+
+        /*
+         * Add some period to $start.
+         */
+        $next = $filter->next($range, clone $start);
+
+        /*
+         * Save in session:
+         */
+        \Session::put('start', $next);
+        return true;
+    }
+
+    /**
+     * @return bool
+     * @throws \Firefly\Exception\FireflyException
+     */
+    public function prev()
+    {
+        /*
+         * Get the start date and the range from the session
+         */
+        $filter = new Filter;
+
+        $range = $filter->setSessionRangeValue();
+        $start = \Session::get('start');
+
+        /*
+         * Substract some period to $start.
+         */
+        $prev = $filter->previous($range, clone $start);
+
+        /*
+         * Save in session:
+         */
+        \Session::put('start', $prev);
+        return true;
+    }
+}