I did it like this and it seems working:
CASE WHEN ROUND({custrecord_imp_stat_parent.trandate} - {today}) > 13 THEN 'Future' WHEN (ROUND({custrecord_imp_stat_parent.trandate} - {today}) <= 13 AND ROUND({custrecord_imp_stat_parent.trandate} - {today}) >= -1) THEN 'Present' ELSE 'Past' END