How to convert birth date records to age with MongoDB

To convert birth date records to age in MongoDB, use the $dateDiff operator or calculate the difference between the current date and birth date using $subtract and $divide operators in an aggregation pipeline.

Syntax

db.collection.aggregate([
    {
        $project: {
            age: {
                $divide: [
                    { $subtract: [new Date(), "$birthDateField"] },
                    (365 * 24 * 60 * 60 * 1000)
                ]
            }
        }
    }
]);

Sample Data

db.demo754.insertMany([
    { "DateOfBirth": new Date("2000-05-03") },
    { "DateOfBirth": new Date("2010-01-21") },
    { "DateOfBirth": new Date("2018-05-03") }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5eae9b2da930c785c834e56f"),
        ObjectId("5eae9b34a930c785c834e570"),
        ObjectId("5eae9b3da930c785c834e571")
    ]
}

Display all documents from the collection ?

db.demo754.find();

{ "_id": ObjectId("5eae9b2da930c785c834e56f"), "DateOfBirth": ISODate("2000-05-03T00:00:00Z") }
{ "_id": ObjectId("5eae9b34a930c785c834e570"), "DateOfBirth": ISODate("2010-01-21T00:00:00Z") }
{ "_id": ObjectId("5eae9b3da930c785c834e571"), "DateOfBirth": ISODate("2018-05-03T00:00:00Z") }

Example: Convert Birth Date to Age

db.demo754.aggregate([
    {
        $project: {
            date: "$DateOfBirth",
            StudentAge: {
                $divide: [
                    { $subtract: [new Date(), "$DateOfBirth"] },
                    (365 * 24 * 60 * 60 * 1000)
                ]
            }
        }
    }
]);

{ "_id": ObjectId("5eae9b2da930c785c834e56f"), "date": ISODate("2000-05-03T00:00:00Z"), "StudentAge": 20.014896543093606 }
{ "_id": ObjectId("5eae9b34a930c785c834e570"), "date": ISODate("2010-01-21T00:00:00Z"), "StudentAge": 10.288869145833333 }
{ "_id": ObjectId("5eae9b3da930c785c834e571"), "date": ISODate("2018-05-03T00:00:00Z"), "StudentAge": 2.003937638984018 }

How It Works

• $subtract calculates the difference between current date and birth date in milliseconds
• $divide converts milliseconds to years by dividing by milliseconds per year
• The formula (365 * 24 * 60 * 60 * 1000) represents milliseconds in a year

Conclusion

Use the $subtract and $divide operators in an aggregation pipeline to convert birth dates to age. This method calculates the precise age difference in years as decimal values.