<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css"> <script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script> <script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script> <!------ Include the above in your HEAD tag ----------> <!-- Button trigger modal --> <button class="btn btn-primary btn-lg" data-toggle="modal" data-target="#myModal">Launch demo modal</button> <!-- Modal --> <div class="modal fade" id="myModal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true"> <div class="modal-center"> <div class="modal-dialog .modal-align-center"> <div class="modal-content"> <div class="modal-header"> <h4 class="modal-title" id="myModalLabel">Modal title</h4> <button type="button" class="close" data-dismiss="modal"><span aria-hidden="true">×</span><span class="sr-only">Close</span> </button> </div> <div class="modal-body">...</div> <div class="modal-footer"> <button type="button" class="btn btn-default" data-dismiss="modal">Close</button> <button type="button" class="btn btn-primary">Save changes</button> </div> </div> </div> </div> </div>

.modal-center { display:table; height: 100%; width: 100%; } .modal-align-center {: table-cell;vertical-align: middle;} .modal-content {height:inherit;margin: 0 auto;}