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# dayofyear
> This page explains how to use the dayofyear function in APL.
Use the `dayofyear` function in APL to extract the day number within the year from a datetime value. The function returns an integer from 1 to 365 (or 1 to 366 in a leap year) representing how far into the year the given date falls.
You can use `dayofyear` to perform year-over-year comparisons by day, analyze seasonal trends, and track how metrics evolve throughout the year. This is especially useful for time-series analysis where you want to align data across multiple years by day number.
Use it when you want to:
* Compare activity or metrics on the same day across different years.
* Identify seasonal trends and patterns in log, trace, or security data.
* Track progress through the year for cumulative reporting.
## For users of other query languages
If you come from other query languages, this section explains how to adjust your existing queries to achieve the same results in APL.
In Splunk SPL, you typically use the `strftime` function with the `%j` specifier to extract the day of the year. In APL, the `dayofyear` function directly returns the day number within the year from a datetime value.
```sql Splunk example theme={null}
... | eval doy=strftime(_time, "%j")
```
```kusto APL equivalent theme={null}
... | extend day_of_year = dayofyear(_time)
```
In ANSI SQL, you often use `EXTRACT(DOY FROM timestamp)` or `DAYOFYEAR(timestamp)`. The APL `dayofyear` function provides the same result, returning an integer from 1 to 366.
```sql SQL example theme={null}
SELECT EXTRACT(DOY FROM timestamp_column) AS day_of_year FROM events;
```
```kusto APL equivalent theme={null}
['dataset']
| extend day_of_year = dayofyear(_time)
```
## Usage
### Syntax
```kusto theme={null}
dayofyear(datetime)
```
### Parameters
| Name | Type | Description |
| -------- | ---------- | ------------------------- |
| datetime | `datetime` | The input datetime value. |
### Returns
An `int` from 1 to 366 representing the day number within the year.
## Use case examples
Track daily request counts across the year to spot high-traffic and low-traffic periods.
**Query**
```kusto theme={null}
['sample-http-logs']
| extend day_of_year = dayofyear(_time)
| summarize request_count = count() by day_of_year
| sort by day_of_year asc
```
[Run in Playground](https://play.axiom.co/axiom-play-qf1k/query?initForm=%7B%22apl%22%3A%22%5B'sample-http-logs'%5D%20%7C%20extend%20day_of_year%20%3D%20dayofyear\(_time\)%20%7C%20summarize%20request_count%20%3D%20count\(\)%20by%20day_of_year%20%7C%20sort%20by%20day_of_year%20asc%22%7D)
**Output**
| day\_of\_year | request\_count |
| ------------- | -------------- |
| 1 | 482 |
| 2 | 531 |
| 3 | 497 |
This query counts the total number of HTTP requests for each day of the year, helping you identify seasonal traffic patterns.
Monitor trace volume trends by day of the year for each service to detect seasonal performance shifts.
**Query**
```kusto theme={null}
['otel-demo-traces']
| extend day_of_year = dayofyear(_time)
| summarize trace_count = count() by day_of_year, ['service.name']
| sort by day_of_year asc
```
[Run in Playground](https://play.axiom.co/axiom-play-qf1k/query?initForm=%7B%22apl%22%3A%22%5B'otel-demo-traces'%5D%20%7C%20extend%20day_of_year%20%3D%20dayofyear\(_time\)%20%7C%20summarize%20trace_count%20%3D%20count\(\)%20by%20day_of_year%2C%20%5B'service.name'%5D%20%7C%20sort%20by%20day_of_year%20asc%22%7D)
**Output**
| day\_of\_year | service.name | trace\_count |
| ------------- | ------------ | ------------ |
| 1 | frontend | 312 |
| 2 | frontend | 287 |
| 3 | frontend | 345 |
This query tracks how trace volume changes day by day throughout the year for each service, revealing seasonal trends.
Find the busiest days of the year for server errors to identify recurring problem periods.
**Query**
```kusto theme={null}
['sample-http-logs']
| where toint(status) >= 500
| extend day_of_year = dayofyear(_time)
| summarize error_count = count() by day_of_year
| sort by error_count desc
```
[Run in Playground](https://play.axiom.co/axiom-play-qf1k/query?initForm=%7B%22apl%22%3A%22%5B'sample-http-logs'%5D%20%7C%20where%20toint\(status\)%20%3E%3D%20500%20%7C%20extend%20day_of_year%20%3D%20dayofyear\(_time\)%20%7C%20summarize%20error_count%20%3D%20count\(\)%20by%20day_of_year%20%7C%20sort%20by%20error_count%20desc%22%7D)
**Output**
| day\_of\_year | error\_count |
| ------------- | ------------ |
| 142 | 87 |
| 98 | 64 |
| 215 | 53 |
This query ranks days of the year by server error count, helping you pinpoint recurring high-error periods.
## List of related functions
* [dayofmonth](/apl/scalar-functions/datetime-functions/dayofmonth): Returns the day number within the month from a datetime.
* [dayofweek](/apl/scalar-functions/datetime-functions/dayofweek): Returns the day of the week as an integer, useful for weekday versus weekend analysis.
* [datetime\_part](/apl/scalar-functions/datetime-functions/datetime-part): Extracts a specific date part (such as day or year) as an integer.
* [monthofyear](/apl/scalar-functions/datetime-functions/monthofyear): Returns the month number from a datetime, useful for monthly grouping.
* [getyear](/apl/scalar-functions/datetime-functions/getyear): Returns the year from a datetime, useful for year-level aggregation.