The $dayOfWeek operator extracts the weekday as an integer from 1 to 7 inside MongoDB aggregation pipelines. Use it to filter weekend traffic, compare Monday vs Friday sales, or group events by weekday pattern.
Date → integer 1–7.
One date argument.
MongoDB numbering.
Uses UTC calendar.
Weekends, weekdays.
Different numbering.
In MongoDB’s aggregation framework, the $dayOfWeek operator takes a date expression and returns an integer from 1 to 7. MongoDB numbers weekdays with Sunday = 1 through Saturday = 7. For example, $dayOfWeek on ISODate("2024-06-15T00:00:00Z") (a Saturday) returns 7.
Do not assume Monday = 1. MongoDB’s $dayOfWeek starts the week on Sunday. For ISO-style numbering (Monday = 1), use $isoDayOfWeek instead.
The $dayOfWeek operator takes a single date expression:
{ $dayOfWeek: <dateExpression> }Date.null when the date is null or missing.$project, $addFields, $match with $expr, or $group.1 — Sunday2 — Monday3 — Tuesday4 — Wednesday5 — Thursday6 — Friday7 — Saturday| Question | Answer |
|---|---|
| Operator type | Aggregation expression operator (date extraction) |
| Arguments | One date expression |
| Return type | Integer (1–7) |
| Week starts on | Sunday (= 1) |
| MongoDB version | 3.4+ |
{ $dayOfWeek: "$orderDate" }Weekday of orderDate
{ $dayOfWeek: ISODate("2024-06-15") }Returns 7
{ $in: [
{ $dayOfWeek: "$d" },
[1, 7]
]}Sun or Sat
{ $eq: [
{ $dayOfWeek: "$d" },
2
]}Monday = 2
Extract weekday numbers, filter weekend orders, find Monday activity, and analyze sales by day of week with $dayOfWeek.
Use an orders collection and add a weekday number from orderDate.
Suppose you have an orders collection with order timestamps:
[
{
"_id": ObjectId("609c26812e9274a86871bc6a"),
"item": "Laptop",
"orderDate": ISODate("2024-06-15T14:30:00Z")
},
{
"_id": ObjectId("609c26812e9274a86871bc6b"),
"item": "Desk",
"orderDate": ISODate("2024-06-17T10:00:00Z")
}
]Extract the weekday integer from each order date:
db.orders.aggregate([
{
$project: {
item: 1,
orderDate: 1,
weekday: { $dayOfWeek: "$orderDate" }
}
}
])7.2.Weekend filters, weekday-only reports, and sales breakdowns by day of week.
Find orders placed on Saturday or Sunday using $expr and $in:
db.orders.find({
$expr: {
$in: [
{ $dayOfWeek: "$orderDate" },
[1, 7]
]
}
})
// 1 = Sunday, 7 = SaturdayWeekend detection in MongoDB uses [1, 7] with $dayOfWeek, not Saturday/Sunday as 6 and 7 in ISO numbering. Double-check your operator before writing filters.
Filter documents where the event occurred on a Monday (weekday = 2):
db.events.aggregate([
{
$match: {
$expr: {
$eq: [
{ $dayOfWeek: "$eventAt" },
2
]
}
}
},
{
$project: {
title: 1,
eventAt: 1
}
}
])Use the weekday reference table when building filters. Monday = 2, Friday = 6. Swap to $isoDayOfWeek if your team expects ISO Monday-first numbering.
See which weekdays drive the most revenue:
db.orders.aggregate([
{
$group: {
_id: { $dayOfWeek: "$orderDate" },
orderCount: { $sum: 1 },
totalAmount: { $sum: "$amount" }
}
},
{ $sort: { _id: 1 } }
])
// _id: 1 → Sunday totals, _id: 7 → Saturday totalsGrouping by $dayOfWeek aggregates all Sundays across every week into one bucket. Add $week or $year to _id when you need per-week breakdowns.
$dayOfWeek WorksThe input expression is evaluated per document — a field, $$NOW, or literal ISODate.
MongoDB determines the weekday in UTC using Sunday = 1 through Saturday = 7.
The number is ready for $match, $group, or conditional logic in pipelines.
Combine with $dayOfMonth, $month, or $isoDayOfWeek for richer calendar logic.
The $dayOfWeek operator is a simple way to extract weekday numbers from BSON dates in MongoDB aggregation pipelines. Its Sunday-first numbering is the main detail beginners must remember when writing weekend or weekday filters.
For ISO Monday-first numbering, use $isoDayOfWeek. For timezone-aware weekdays, use $dateToParts with a timezone field. Next in the series: $dayOfYear for day-of-year extraction.
$isoDayOfWeek when your team expects ISO numbering$in: [1, 7]$dayOfWeek$dayOfWeek with $dayOfMonth$dayOfWeek and $isoDayOfWeek in one dashboard without labels$dateFromString first$dayOfWeekUse these points when extracting weekdays from dates in MongoDB.
Date → 1–7.
PurposeDate expression.
SyntaxKey numbering rule.
OutputDefault timezone.
NoteMonday-first vs Sun-first.
ImportantMove on to $dayOfYear to extract the day number within a year, or review $dayOfMonth for calendar-day extraction.
5 people found this page helpful