[{month:"January",start:ISODate("2021-01-01"),end:ISODate("2021-01-31")},{month:"February",start:ISODate("2021-02-01"),end:ISODate("2021-03-28")},{month:"March",start:ISODate("2021-03-01"),end:ISODate("2022-03-31")},]

db.collection.aggregate([{$project:{Start:"$start",End:"$end",years:{$dateDiff:{startDate:"$start",endDate:"$end",unit:"year"}},months:{$dateDiff:{startDate:"$start",endDate:"$end",unit:"month"}},days:{$dateDiff:{startDate:"$start",endDate:"$end",unit:"day"}},_id:0}}])