Checkboxes are not checked in angular2

I have list of object to show for checkboxes

public weeks = [
{ value: 'All', display: 'All',isChecked: false },
{ value: 'Mon', display: 'Mon',isChecked: false },
{ value: 'Tue', display: 'Tue',isChecked: false },
{ value: 'Wed', display: 'Wed',isChecked: false },
{ value: 'Thu', display: 'Thu',isChecked: false },
{ value: 'Fri', display: 'Fri',isChecked: false }
];

app.component.html

      <span *ngFor="let month of months">
        <label>
          <input type="checkbox" name="months" [(ngModel)]="month.isChecked" class="months" >
          
        </label>
      </span>

Issue is that it now bind selected checkboxes .

app.component.ts

this.weeks.forEach((month) => {
    var i = this.selected_weeks.indexOf(month.week);
    if(i != -1) {
      week.isChecked = true;
      console.log(week.isChecked);
    }
  });

in component it mark that object true but in view it not selected