[{"id":1,"resetPassword":[{code:"1",expiresAt:ISODate("2020-02-01T00:00:00Z"),createdAt:ISODate("2020-01-01T00:00:00Z")},{code:"2",expiresAt:ISODate("2020-03-01T00:00:00Z"),createdAt:ISODate("2020-02-01T00:00:00Z")},{code:"3",expiresAt:ISODate("2020-04-01T00:00:00Z"),createdAt:ISODate("2020-03-01T00:00:00Z")},{code:"4",expiresAt:ISODate("2020-05-01T00:00:00Z"),createdAt:ISODate("2020-04-01T00:00:00Z")},{code:"5",expiresAt:ISODate("2020-06-01T00:00:00Z"),createdAt:ISODate("2020-05-01T00:00:00Z")},{code:"6",expiresAt:ISODate("2020-07-01T00:00:00Z"),createdAt:ISODate("2020-06-01T00:00:00Z")},{code:"7",expiresAt:ISODate("2020-08-01T00:00:00Z"),createdAt:ISODate("2020-07-01T00:00:00Z")},{code:"8",expiresAt:ISODate("2020-09-01T00:00:00Z"),createdAt:ISODate("2020-08-01T00:00:00Z")},{code:"9",expiresAt:ISODate("2020-10-01T00:00:00Z"),createdAt:ISODate("2020-09-01T00:00:00Z")}]}]

db.collection.aggregate([{$match:{"id":1}},{$project:{totalValidResetCodes:{$reduce:{input:"$resetPassword",initialValue:0,in:{$add:["$$value",{$cond:[{$gt:["$$this.expiresAt",ISODate("2020-09-01T00:00:00Z")]},1,0]}]}}}}}])