table{
width: 300px;
table-layout: fixed;
}
#tbody{
display: block;
height: 100px;
overflow-y: auto;
width: 300px;
}
#tbody tr{
display: table;
width: 100%;
table-layout: fixed;
}
<table border="1">
<thead>
<tr>
<th colspan="2">Month</th>
<th colspan="2">Savings</th>
</tr>
<tr>
<th>Month</th>
<th>Savings</th>
<th>Month</th>
<th>Savings</th>
</tr>
</thead>
<tbody id="tbody" >
<tr>
<td>January</td>
<td>$100</td>
<td>January</td>
<td>$100</td>
</tr>
<tr>
<td>January</td>
<td>$100</td>
<td>January</td>
<td>$100</td>
</tr>
</tbody>
<tfoot>
<tr>
<td>Sum</td>
<td>$180</td>
<td>Sum</td>
<td>$180</td>
</tr>
</tfoot>
</table>
