<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.7.9/angular.min.js"></script>

<div ng-app="myApp" ng-controller="myCtrl">
  <input type="date" ng-model="currentDate" ng-change="calculateDays()">
  <p>{{ days }}</p>
</div>

<script>
  var app = angular.module('myApp', []);
  app.controller('myCtrl', function($scope) {
    $scope.calculateDays = function() {
      var currentDate = new Date($scope.currentDate);
      var futureDate = new Date(currentDate.getTime() + 30 * 24 * 60 * 60 * 1000);
      var diff = Math.ceil((futureDate - currentDate) / (1000 * 60 * 60 * 24));
      $scope.days = diff;
    };
  });
</script>