Database
[{_id:"112233",item:"CAR",startdate:ISODate("2022-03-16T07:38:08.466Z"),enddate:ISODate("2022-03-16T08:38:08.466Z")},{_id:"11222333",item:"BIKE",startdate:ISODate("2022-02-16T07:38:08.466Z"),enddate:ISODate("2022-02-14T08:38:08.466Z")},{_id:"1122333243",item:"CAR",startdate:ISODate("2022-01-16T07:38:08.466Z"),enddate:ISODate("2022-02-16T01:38:08.466Z")},{_id:"12312233",item:"BUS",startdate:ISODate("2021-03-16T07:38:08.466Z"),enddate:ISODate("2021-03-16T08:38:08.466Z")}]
Query
db.collection.aggregate([{$match:{item:"CAR"}},{$set:{diff:{$dateDiff:{startDate:"$startdate",endDate:"$enddate",unit:"day"}}}}])