<div class="full-height">
   <nav class="navbar navbar-expand-lg navbar-light bg-light">
      <a class="navbar-brand" href="#">Logo</a><button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation"><span class="navbar-toggler-icon"></span></button>
      <div class="collapse navbar-collapse" id="navbarSupportedContent">
         <ul class="navbar-nav ml-auto">
            <li class="nav-item"><a class="nav-link active" aria-current="page" href="/">Home</a></li>
         </ul>
      </div>
   </nav>
   <div class="container h-100">
      <div class="row h-100 justify-content-center align-items-center">
         <form class="col-12">
            <div class="form-group"><label for="formGroupExampleInput">Example label</label><input type="text" class="form-control" id="formGroupExampleInput" placeholder="Example input"></div>
            <div class="form-group"><label for="formGroupExampleInput2">Another label</label><input type="text" class="form-control" id="formGroupExampleInput2" placeholder="Another input"></div>
         </form>
      </div>
   </div>
</div>

body, html, .full-height {
  height: 100%;
}