[{"_id":"KPu78LNXYKfraRF94","aboutPage":{"birthDay":NumberInt(27),"birthMonth":NumberInt(5)}},{"_id":"shouldReturn","aboutPage":{"birthDay":NumberInt(18),"birthMonth":NumberInt(11)}}]

db.collection.aggregate([{$set:{birthDate:{"$dateFromParts":{"year":{"$year":"$$NOW"},"month":"$aboutPage.birthMonth","day":"$aboutPage.birthDay"}}}},{"$set":{"daysFromToday":{"$dateDiff":{startDate:"$birthDate",endDate:"$$NOW",unit:"day"}}}},{"$match":{daysFromToday:-1}},{"$unset":["daysFromToday","birthDate"]}])