MongoDB $subtract Operator (original) (raw)

Last Updated : 15 Apr, 2026

The $subtract operator in MongoDB is an aggregation arithmetic operator used to subtract numbers and perform date/time calculations, helping transform fields in MongoDB queries.

• Subtracts two numbers and returns the difference.
• Subtracts two dates and returns the difference in milliseconds.
• Subtracts milliseconds from a date and returns a new date.
• Takes exactly two expressions: { $subtract: [expr1, expr2] }.
• Second value is subtracted from the first.
• Supports number–number, date–date (returns milliseconds), and date–number (subtracts milliseconds from date).

Syntax

{ $subtract: [ , ] }

• ****$subtract:** MongoDB aggregation operator for subtraction.
• **[ ... ]: Array containing exactly two values.
• ****:** The base value (number or date).
• ****:** The value to subtract from the first.
• **Type compatibility: Expressions must be compatible (numbers or dates).

Examples of MongoDB $subtract Operator

In the following examples, we are working with:

• **Database: GeeksforGeeks
• **Collection: Employee
• **Document: four documents that contain the details of the employees in the form of field-value pairs.

Example 1: Subtract Numbers

Subtract the value of firstSalary field from the value of secondSalary field using $subtract operator.

**Query:

db.Employee.aggregate([
{ $match: { department: "Development" } },
{
$project: {
result: { subtract:["subtract: ["subtract:["secondSalary", "$firstSalary"] }
}
}
])

**Output:

Example 2: Subtract Two Dates

Subtract two dates, i.e, the value of projectStartDate field from the value of projectEndDate field using a $subtract operator.

**Query:

db.Employee.aggregate([
{ $match: { department: "Testing" } },
{
$project: {
diffResult: { subtract:["subtract: ["subtract:["projectEndDate", "$projectStartDate"] }
}
}
])

**Output:

Example 3: Subtract Milliseconds from a Date

Subtract 5*24*60*60000 milliseconds (i.e., 5 days) from the value of projectEndDate field using a $subtract operator.

**Query:

db.Employee.aggregate([
{ $match: { department: "Testing" } },
{ $project: {
newprojectEndDate: {
subtract:["subtract: ["subtract:["projectEndDate", 5 * 24 * 60 * 60000]
}
}
}
])

**Output:

Use Cases of MongoDB $subtract Operator

The $subtract operator is useful for various scenarios, including:

• **Age calculation: Find age using the difference between the current date and birth date.
• **Time-based calculations: Measure the duration between two events.
• **Date manipulation: Add or subtract days, months, or years from a date.
• **Financial calculations: Compute differences between amounts (e.g., salary, balance).