diff --git a/src/addcalendar.php b/src/addcalendar.php
new file mode 100644
index 0000000..fff0536
--- /dev/null
+++ b/src/addcalendar.php
@@ -0,0 +1,132 @@
+<?php
+require_once("core.php");
+security::checkType(security::ADMIN);
+
+if (!isset($_GET["id"])) {
+  security::go("calendars.php");
+}
+
+$category = $_GET["id"];
+
+$categoryd = categories::get($category);
+
+if ($categoryd === false && $category != -1) {
+  security::go("calendars.php");
+}
+
+if ($category == -1) {
+  $categoryd = array("name" => "Calendario por defecto");
+}
+
+// These checks are just to know whether the user filled in the form or not.
+// Thus, I added true as the third parameter to not display debug information when they fail.
+$newCalendar = security::checkParams("GET", [
+  ["begins", security::PARAM_ISDATE],
+  ["ends", security::PARAM_ISDATE]
+], true);
+
+$importCalendar = security::checkParams("POST", [
+  ["import", security::PARAM_NEMPTY]
+], true);
+
+$calendarEditor = ($newCalendar || $importCalendar);
+
+if ($importCalendar) {
+  $calendar = json_decode($_POST["import"], true);
+
+  if (json_last_error() !== JSON_ERROR_NONE || !isset($calendar["begins"]) || !isset($calendar["ends"]) || !isset($calendar["calendar"])) {
+    security::go("addcalendar.php?id=".(int)$category."&msg=jsoninvalid");
+  }
+}
+
+$mdHeaderRowBefore = visual::backBtn(($calendarEditor ? "addcalendar.php?id=".(int)$category : "calendars.php"));
+?>
+<!DOCTYPE html>
+<html>
+<head>
+  <title><?php echo $conf["appName"]; ?></title>
+  <?php visual::includeHead(); ?>
+  <link rel="stylesheet" href="css/dashboard.css">
+  <link rel="stylesheet" href="css/calendar.css">
+</head>
+<?php visual::printBodyTag(); ?>
+  <div class="mdl-layout mdl-js-layout mdl-layout--fixed-header mdl-layout--fixed-drawer">
+    <?php visual::includeNav(); ?>
+    <main class="mdl-layout__content">
+      <div class="page-content">
+        <div class="main mdl-shadow--4dp">
+          <h2>Añadir calendario a &ldquo;<?=security::htmlsafe($categoryd["name"])?>&rdquo;</h2>
+          <?php
+          if ($calendarEditor) {
+            if ($newCalendar) {
+              $current = new DateTime($_GET["begins"]);
+              $ends = new DateTime($_GET["ends"]);
+            } else {
+              $current = new DateTime();
+              $current->setTimestamp((int)$calendar["begins"]);
+              $ends = new DateTime();
+              $ends->setTimestamp((int)$calendar["ends"]);
+            }
+
+            if ($current->diff($ends)->invert === 1) {
+              security::go("addcalendar.php?id=".(int)$category."&msg=inverted");
+            }
+
+            if (calendars::checkOverlap($category, $current->getTimestamp(), $ends->getTimestamp())) {
+              security::go("addcalendar.php?id=".(int)$category."&msg=overlap");
+            }
+
+            if ($importCalendar) {
+              echo "<p>Este es el calendario que has importado. Ahora puedes hacer las modificaciones que creas oportunas y añadirlo.</p>";
+            }
+            ?>
+            <form action="doaddcalendar.php" method="POST">
+              <input type="hidden" name="id" value="<?=(int)$category?>">
+              <input type="hidden" name="begins" value="<?=security::htmlsafe(($newCalendar ? $_GET["begins"] : $current->format("Y-m-d")))?>">
+              <input type="hidden" name="ends" value="<?=security::htmlsafe(($newCalendar ? $_GET["ends"] : $ends->format("Y-m-d")))?>">
+              <?php
+              calendarsView::renderCalendar($current, $ends, ($newCalendar ? function ($timestamp, $id, $dow, $dom, $extra) {
+                return (($dow >= 6 && $id == calendars::TYPE_FESTIU) || $dow < 6 && $id == calendars::TYPE_LECTIU);
+              } : function ($timestamp, $id, $dow, $dom, $extra) {
+                return ($extra[$timestamp] == $id);
+              }), false, ($newCalendar ? false : $calendar["calendar"]));
+              ?>
+              <button class="mdl-button mdl-js-button mdl-button--raised mdl-js-ripple-effect mdl-button--accent">Añadir</button>
+            </form>
+            <?php
+          } else {
+            ?>
+            <p>Introduce las fechas de inicio y fin del calendario que quieres configurar:</p>
+            <form action="addcalendar.php" method="GET">
+              <input type="hidden" name="id" value="<?=(int)$category?>">
+              <p><label for="begins">Fecha inicio:</label> <input type="date" id="begins" name="begins" required> <label for="ends">Fecha fin:</label> <input type="date" id="ends" name="ends" required></p>
+              <p><button class="mdl-button mdl-js-button mdl-button--raised mdl-js-ripple-effect mdl-button--accent">Empezar a configurar el calendario</button></p>
+            </form>
+            <hr>
+            <p>Alternativamente, puedes importar un calendario para usarlo como plantilla y editarlo antes de crearlo:</p>
+            <form action="addcalendar.php?id=<?=(int)$category?>" method="POST">
+              <div class="mdl-textfield mdl-js-textfield mdl-textfield--floating-label">
+                <textarea class="mdl-textfield__input" name="import" id="import" rows="3" data-required></textarea>
+                <label class="mdl-textfield__label" for="import">Código JSON del calendario original</label>
+              </div>
+              <p><button class="mdl-button mdl-js-button mdl-button--raised mdl-js-ripple-effect mdl-button--accent">Importar calendario</button></p>
+            </form>
+            <?php
+          }
+          ?>
+        </div>
+      </div>
+    </main>
+  </div>
+
+  <script src="js/calendar.js"></script>
+
+  <?php
+  visual::smartSnackbar([
+    ["inverted", "La fecha de inicio debe ser anterior a la fecha de fin."],
+    ["overlap", "El calendario que intentabas añadir se solapa con uno ya existente."],
+    ["jsoninvalid", "El código JSON del calendario que estás importando es incorrecto."]
+  ]);
+  ?>
+</body>
+</html>