Jquery insert new row into table at a certain index

You can use .eq() and .after() like this:

$('#my_table > tbody > tr').eq(i-1).after(html);

The indexes are 0 based, so to be the 4th row, you need i-1, since .eq(3) would be the 4th row, you need to go back to the 3rd row (2) and insert .after() that.