> For the complete MongoDB documentation index, see www.mongodb.com/docs/llms.txt

# $dateAdd (expression operator)

## Definition

**New in version 5.0**

Increments a [`Date()`](https://www.mongodb.com/docs/manual/reference/mongodb-extended-json.md#mongodb-bsontype-Date) object by a specified number of time units.

The [`$dateAdd`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/dateadd.md#mongodb-expression-exp.-dateAdd) expression has the following syntax:

```javascript
{
   $dateAdd: {
      startDate: <Expression>,
      unit: <Expression>,
      amount: <Expression>,
      timezone: <tzExpression>
   }
}
```

Returns a `Date()`. The `startDate` can be any expression that resolves to type Date, Timestamp or ObjectId. No matter which data type is used as input, the value returned will be a `Date()` object.

| Field | Required/Optional | Description |
| --- | --- | --- |
| `startDate` | Required | The beginning date, in UTC, for the addition operation. The `startDate` can be any [expression](https://www.mongodb.com/docs/manual/reference/mql/expressions.md#std-label-aggregation-expressions) that resolves to a [Date](https://www.mongodb.com/docs/manual/reference/bson-types.md#std-label-document-bson-type-date), a [Timestamp](https://www.mongodb.com/docs/manual/reference/bson-types.md#std-label-document-bson-type-timestamp), or an [ObjectID.](https://www.mongodb.com/docs/manual/reference/bson-types.md#std-label-document-bson-type-object-id) |
| `unit` | Required | The `unit` used to measure the `amount` of time added to the `startDate`. The `unit` is an [expression](https://www.mongodb.com/docs/manual/reference/mql/expressions.md#std-label-aggregation-expressions) that resolves to one of the following strings: `year`; `quarter`; `week`; `month`; `day`; `hour`; `minute`; `second`; `millisecond` IMPORTANT: Starting in MongoDB 8.3, if `unit` is not `"millisecond"` and the input date is before `ISODate("1970-01-01T00:00:00Z")`, the result is one second greater than in previous versions of MongoDB. |
| `amount` | Required | The number of `units` added to the `startDate`. The `amount` is an [expression](https://www.mongodb.com/docs/manual/reference/mql/expressions.md#std-label-aggregation-expressions) that resolves to an integer or long. The `amount` can also resolve to an integral decimal or a double if that value can be converted to a long without loss of precision. |
| `timezone` | Optional | The timezone to carry out the operation. `<tzExpression>` must be a valid [expression](https://www.mongodb.com/docs/manual/reference/mql/expressions.md#std-label-aggregation-expressions) that resolves to a string formatted as either an [Olson Timezone Identifier](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones) or a [UTC Offset](https://en.wikipedia.org/wiki/List_of_UTC_time_offsets): Olson Timezone Identifier: for example, `"America/New_York"`, `"Europe/London"`, `"GMT"`; UTC Offset: for example, `"+04:45"`, `"-0530"`, `"+03"` If you omit `timezone`, the result is displayed in `UTC`. |

For more information on expressions and types see [Expressions](https://www.mongodb.com/docs/manual/reference/mql/expressions.md#std-label-aggregation-expressions) and [MongoDB BSON Types.](https://www.mongodb.com/docs/manual/reference/bson-types.md#std-label-bson-types)

## Behavior

### Time Measurement

MongoDB follows prevaling database usage and works with time in UTC. The `dateAdd` expression always takes a `startDate` in UTC and returns a result in UTC. If the `timezone` is specified, the calculation will be done using the specified `timezone`. The timezone is especially important when a calculation involves Daylight Savings Time (DST).

If the `unit` is a `month`, or larger the operation adjusts to account for the last day of the month. Adding one `month` on the last day of October, for example, demonstrates the "last-day-of-the-month" adjustment.

```javascript
{
   $dateAdd:
      {
         startDate: ISODate("2020-10-31T12:10:05Z"),
         unit: "month",
         amount: 1
      }
}
```

Notice that the date returned, `ISODate("2020-11-30T12:10:05Z")`, is the 30th and not the 31st since November has fewer days than October.

### Time Zone

When using an Olson Timezone Identifier in the `<timezone>` field, MongoDB applies the DST (Daylight Savings Time) offset if applicable for the specified timezone.

For example, consider a `sales` collection with the following document:

```javascript&#xA;
 db.sales.insertOne(
  {
   "_id" : 1,
   "item" : "abc",
   "price" : 10,
   "quantity" : 2,
   "date" : ISODate("2014-01-01T08:15:39.736Z")
  }
)
```

The following aggregation illustrates how MongoDB handles the DST offset for the Olson Timezone Identifier. The example uses the [`$hour`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/hour.md#mongodb-expression-exp.-hour) and [`$minute`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/minute.md#mongodb-expression-exp.-minute) operators to return the corresponding portions of the `date` field:

```javascript
db.sales.aggregate([
{
   $project: {
      "nycHour": {
         $hour: { date: "$date", timezone: "-05:00" }
       },
       "nycMinute": {
          $minute: { date: "$date", timezone: "-05:00" }
       },
       "gmtHour": {
          $hour: { date: "$date", timezone: "GMT" }
       },
       "gmtMinute": {
          $minute: { date: "$date", timezone: "GMT" } },
       "nycOlsonHour": {
          $hour: { date: "$date", timezone: "America/New_York" }
       },
       "nycOlsonMinute": {
          $minute: { date: "$date", timezone: "America/New_York" }
       }
   }
}])
```

The operation returns the following result:

```javascript
{
   "_id": 1,
   "nycHour" : 5,
   "nycMinute" : 24,
   "gmtHour" : 10,
   "gmtMinute" : 24,
   "nycOlsonHour" : 6,
   "nycOlsonMinute" : 24
}
```

## Examples

### Add a Future Date

Consider a collection of customer orders with these documents:

```javascript
db.shipping.insertMany(
  [
     { custId: 456, purchaseDate: ISODate("2020-12-31") },
     { custId: 457, purchaseDate: ISODate("2021-02-28") },
     { custId: 458, purchaseDate: ISODate("2021-02-26") }
  ]
)
```

The normal shipping time is 3 days. You can use `$dateAdd` in an aggregation pipeline to set an `expectedDeliveryDate` 3 days in the future.

```javascript
db.shipping.aggregate(
   [
      {
         $project:
            {
               expectedDeliveryDate:
                  {
                     $dateAdd:
                        {
                           startDate: "$purchaseDate",
                           unit: "day",
                           amount: 3
                        }
                  }
            }
       },
       {
          $merge: "shipping"
       }
    ]
 )
```

After adding 3 days to the `purchaseDate` with `$dateAdd` in the [`$project`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/project.md#mongodb-pipeline-pipe.-project) stage, the [`$merge`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/merge.md#mongodb-pipeline-pipe.-merge) stage updates the original documents with the `expectedDeliveryDate`.

The resulting documents look like this:

```javascript
{
   "_id" : ObjectId("603dd4b2044b995ad331c0b2"),
   "custId" : 456,
   "purchaseDate" : ISODate("2020-12-31T00:00:00Z"),
   "expectedDeliveryDate" : ISODate("2021-01-03T00:00:00Z")
}
{
   "_id" : ObjectId("603dd4b2044b995ad331c0b3"),
   "custId" : 457,
   "purchaseDate" : ISODate("2021-02-28T00:00:00Z"),
   "expectedDeliveryDate" : ISODate("2021-03-03T00:00:00Z")
}
{
    "_id" : ObjectId("603dd4b2044b995ad331c0b4"),
   "custId" : 458,
   "purchaseDate" : ISODate("2021-02-26T00:00:00Z"),
   "expectedDeliveryDate" : ISODate("2021-03-01T00:00:00Z")
}
```

### Filter on a Date Range

Update the `shipping` collection from the last example with this code to add delivery dates to the documents:

```javascript
db.shipping.updateOne(
   { custId: 456 },
   { $set: { deliveryDate: ISODate( "2021-01-10" ) } }
)

db.shipping.updateOne(
  { custId: 457 },
  { $set: { deliveryDate:  ISODate( "2021-03-01" ) } }
)

db.shipping.updateOne(
   { custId: 458 },
   { $set: { deliveryDate:  ISODate( "2021-03-02" ) } }
)
```

You want to find late shipments. Use `$dateAdd` in a [`$match`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/match.md#mongodb-pipeline-pipe.-match) stage to create a filter that matches documents in a range of dates defined by a starting point (`$purchaseDate`) and a time period given by `$dateAdd`.

```javascript
db.shipping.aggregate(
   [
      {
         $match:
            {
               $expr:
                  {
                     $gt:
                        [ "$deliveryDate",
                          {
                             $dateAdd:
                                {
                                   startDate: "$purchaseDate",
                                   unit: "day",
                                   amount: 5
                                }
                           }
                        ]
                  }
            }
       },
       {
          $project:
             {
                _id: 0,
                custId: 1,
                purchased:
                   {
                       $dateToString:
                          {
                             format: "%Y-%m-%d",
                             date: "$purchaseDate"
                          }
                   },
                delivery:
                   {
                      $dateToString:
                         {
                            format: "%Y-%m-%d",
                            date: "$deliveryDate"
                         }
                   }
             }
       }
   ]
)
```

The [`$match`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/match.md#mongodb-pipeline-pipe.-match) stage uses [`$gt`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/gt.md#mongodb-expression-exp.-gt) and `$dateAdd` in an expression ([`$expr`](https://www.mongodb.com/docs/manual/reference/operator/query/expr.md#mongodb-query-op.-expr)) to compare the actual `deliveryDate` with an expected date. Documents with delivery dates more than 5 days after the `purchaseDate` are passed on to the [`$project`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/project.md#mongodb-pipeline-pipe.-project) stage.

The [`$project`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/project.md#mongodb-pipeline-pipe.-project) stage uses the [`$dateToString`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/datetostring.md#mongodb-expression-exp.-dateToString) expression to convert the dates to a more readable format. Without the conversion, MongoDB returns the date in [ISODate](https://www.mongodb.com/docs/manual/reference/glossary.md#std-term-ISODate) format and assumes a UTC timezone.

In this example only one record is returned:

```javascript
{ "custId" : 456, "purchased" : "2020-12-31", "delivery" : "2021-01-10" }
```

### Adjust for Daylight Savings Time

All dates are stored internally in UTC time. When a `timezone` is specified, `$dateAdd` uses local time to carry out the calculations. The results are displayed in UTC.

You have customers in several timezones and you want to see what effect daylight savings time might have on your billing periods if you bill by `day` or by `hour`.

Create this collection of connection times:

```javascript
db.billing.insertMany(
   [
      {
         location: "America/New_York",
         login: ISODate("2021-03-13T10:00:00-0500"),
         logout: ISODate("2021-03-14T18:00:00-0500")
      },
      {
         location: "America/Mexico_City",
         login: ISODate("2021-03-13T10:00:00-00:00"),
         logout: ISODate("2021-03-14T08:00:00-0500")
      }
   ]
)
```

First add 1 day, then add 24 hours to the `login` dates in each document.

```javascript
db.billing.aggregate(
   [
      {
         $project:
            {
               _id: 0,
               location: 1,
               start:
                  {
                     $dateToString:
                        {
                           format: "%Y-%m-%d %H:%M",
                           date: "$login"
                        }
                  },
               days:
                  {
                     $dateToString:
                        {
                           format: "%Y-%m-%d %H:%M",
                           date:
                              {
                                 $dateAdd:
                                    {
                                       startDate: "$login",
                                       unit: "day",
                                       amount: 1,
                                       timezone: "$location"
                                    }
                              }
                        }
                  },
               hours:
                  {
                     $dateToString:
                        {
                           format: "%Y-%m-%d %H:%M",
                           date:
                              {
                                 $dateAdd:
                                 {
                                    startDate: "$login",
                                    unit: "hour",
                                    amount: 24,
                                    timezone: "$location"
                                 }
                              }
                        }
                  },
               startTZInfo:
                  {
                     $dateToString:
                        {
                           format: "%Y-%m-%d %H:%M",
                           date: "$login",
                           timezone: "$location"
                        }
                  },
               daysTZInfo:
                  {
                     $dateToString:
                        {
                           format: "%Y-%m-%d %H:%M",
                           date:
                              {
                                 $dateAdd:
                                    {
                                       startDate: "$login",
                                       unit: "day",
                                       amount: 1,
                                       timezone: "$location"
                                    }
                              },
                           timezone: "$location"
                        }
                  },
               hoursTZInfo:
                  {
                     $dateToString:
                        {
                           format: "%Y-%m-%d %H:%M",
                           date:
                              {
                                 $dateAdd:
                                    {
                                       startDate: "$login",
                                       unit: "hour",
                                       amount: 24,
                                       timezone: "$location"
                                    }
                              },
                           timezone: "$location"
                        }
                  },
            }
      }
   ]
).pretty()
```

The [`$dateToString`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/datetostring.md#mongodb-expression-exp.-dateToString) expression reformats the output for readability. Results are summarized here:

| Field | New York | Mexico City |
| --- | --- | --- |
| Start | 2021-03-13 15:00 | 2021-03-13 10:00 |
| Start, TZ Info | 2021-03-13 10:00 | 2021-03-13 04:00 |
| 1 Day | 2021-03-14 14:00 | 2021-03-14 10:00 |
| 1 Day, TZ Info | 2021-03-14 10:00 | 2021-03-14 04:00 |
| 24 Hours | 2021-03-14 15:00 | 2021-03-14 10:00 |
| 24 Hours, TZ Info | 2021-03-14 11:00 | 2021-03-14 04:00 |

The chart highlights several points:

- Unformatted dates are returned in UTC. The `$login` for New York is UTC -5, however the `start`, `days`, and `hours` rows display the time in UTC.

- March 14th is the start of DST in New York, but not in Mexico. The calculated time is adjusted when a location switches to DST and crosses from one `day` to the next.

- DST modifies the length of the `day`, not the `hour`. There is no DST change for `hours`. There is an only an adjustment for DST when the measurement `unit` is `day` or larger and the computation crosses a clock change in the specified `timezone`.

**See also:**

[`$dateSubtract`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/datesubtract.md#mongodb-expression-exp.-dateSubtract), [`$dateDiff`](https://www.mongodb.com/docs/manual/reference/operator/aggregation/datediff.md#mongodb-expression-exp.-dateDiff)