View _AddEstEffort.cshtml (Modal implementation using Partial View) 

@model LMSPriorTool.ViewModels.EstimatedEffortViewModel

<div class="modal-header">
    <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
    <h3>Add new Estimated Effort</h3>
</div>

@using (Html.BeginForm("AddEstimatedEffort", "Project", FormMethod.Post, new { @class = "modal-form" }))
{
    @Html.ValidationSummary()

    <div class="modal-body">
        <div class="row-fluid">
             <div>
                @Html.LabelFor(x => x.ProjectId)
                @Html.EditorFor(x => x.ProjectId)
            </div>
            <div>
                @Html.LabelFor(x => x.Cost)
                @Html.EditorFor(x => x.Cost)
            </div>
        </div>
    </div>
   
    <div class="modal-footer">
        <button class="btn btn-primary" type="submit">Save</button>
        <button class="btn" data-dismiss="modal" aria-hidden="true">Close</button>
    </div>
}

View: Layout.cshtml (Included link to open modal)
@Html.ActionLink("Add Estimated Effort", "AddEstimatedEffort", new { projectId = Model.ProjectId }, new { id = "btnAddEstimatedEffort", @class = "btn btn-info pull-right" })

ViewModel: EstimatedEffortViewModel
public class EstimatedEffortViewModel
    {
        public int Cost { get; set; }
        public int ProjectId { get; set; }
    }

Controller: ProjectController.cs
	
        public ActionResult AddEstimatedEffort(int projectId = 1)
        {
            EstimatedEffortViewModel efvm = new EstimatedEffortViewModel
            {
                ProjectId = projectId,
            };
            return PartialView("_AddEstEffort", efvm);
        }

        [HttpPost]
        public ActionResult AddEstimatedEffort(EstimatedEffortViewModel estimatedEffortVM)
        {
            Project project = db.Projects.Find(estimatedEffortVM.ProjectId);
            if (project == null)
            {
                return HttpNotFound();
            }
            project.EstimatedEfforts.Add(new EstimatedEffort
            {
                EstimatedEffortId = estimatedEffortVM.EstimatedEffortId,
                Cost = estimatedEffortVM.Cost,
            });
            db.SaveChanges();

            return RedirectToAction("Details", new { id = estimatedEffortVM.ProjectId });
        }

JavaScript to open Modal:
<script type="text/javascript">
    $(function () {

        //Optional: turn the chache off
        $.ajaxSetup({ cache: false });

        $('#btnAddEstimatedEffort').click(function () {
            $('#dialogContent').load(this.href, function () {
                $('#dialogDiv').modal({
                    backdrop: 'static',
                    keyboard: true
                }, 'show');
                bindForm(this);
            });
            return false;
        });
    });

    function bindForm(dialog) {
        $('form', dialog).submit(function () {
            $.ajax({
                url: this.action,
                type: this.method,
                data: $(this).serialize(),
                success: function (result) {
                    if (result.success) {
                        $('#dialogDiv').modal('hide');
                        // Refresh:
                        // location.reload();
                    } else {
                        $('#dialogContent').html(result);
                        bindForm();
                    }
                }
            });
            return false;
        });
    }