Haces el formulario de los meses
y simplemente insertas el mes en tu consulta
Código PHP:
$query = "SELECT vol_corr AS codigo, vol_fecha AS fecha, tipo_mov AS mov, ifnull(vol_depus, 0) AS dep, ifnull(vol_retus, 0) AS ret,
(SELECT SUM(ifnull(vol_depus, 0)-ifnull(vol_retus, 0))
FROM bono
WHERE vol_corr <= codigo AND vol_cod = $cod) AS saldo
FROM bono
WHERE vol_cod = $cod AND vol_fecha >= '".date("Y")."/".$_POST['nombre_del campo_del_formulario']."/01'
GROUP BY codigo"
Algo así