Bootstrap 4 responsive tables won't take up 100% width

The following WON'T WORK. It causes another issue. It will now do the 100% width but it won't be responsive on smaller devices:

.table-responsive {
    display: table;
}

All these answers introduced another problem by recommending display: table;. The only solution as of right now is to use it as a wrapper:

<div class="table-responsive">
  <table class="table">
...
 </table>
</div>

This solution worked for me:

just add another class into your table element: w-100 d-block d-md-table

so it would be : <table class="table table-responsive w-100 d-block d-md-table">

for bootstrap 4 w-100 set the width to 100% d-block (display: block) and d-md-table (display: table on min-width: 576px)

Bootstrap 4 display docs

If you're using V4.1, and according to their docs, don't assign .table-responsive directly to the table. The table should be .table and if you want it to be horizontally scrollable (responsive) add it inside a .table-responsive container (a <div>, for instance).

Responsive tables allow tables to be scrolled horizontally with ease. Make any table responsive across all viewports by wrapping a .table with .table-responsive.

<div class="table-responsive">
  <table class="table">
  ...
  </table>
</div>

doing that, no extra css is needed.

In the OP's code, .table-responsive can be used alongside with the .col-md-12 on the outside .