Looker Studio Function : DAY
Category: DATE function
The DAY function in Looker Studio is a powerful date function used to extract the day of the month from a given date. This allows analysts to perform day-level time-based calculations, helping with more granular data analysis and trend tracking.
Purpose of the DAY Function
1. Data Distribution Analysis :
The DAY function helps to analyze how data points are spread across different days in a month. By segmenting data daily, you can uncover trends and identify peak activity periods.
2. Customer Segmentation :
Marketers can segment customers based on the day of their activity, purchases, or sign-ups. This helps in understanding user behavior and sending personalized communication.
3. Decision Making :
With day-level insights, businesses can make informed decisions on staffing, marketing, and inventory management by identifying which days yield higher conversions or traffic.
Type of Calculation & Practical Use Cases
✅ Performance Benchmarking
Compare daily sales, engagement, or KPIs to measure performance across time.
✅ Customer Segmentation
Segment users based on the day of signup, purchase, or engagement.
✅ Time Series Analysis
Analyze trends by breaking down data by individual days for granular insight.
DAY(date_expression)
| Parameter | Type | Description |
|---|---|---|
date_expression | Date | The date field from which to extract the day. |
How Does the DAY Function Work?
The DAY function extracts just the day portion (1–31) from a full date. It runs during the data transformation phase in Looker Studio, making your dashboards and charts more dynamic for date-based analysis.
✅ When Should You Use It?
Use the DAY function when you need daily breakdowns of performance, identify day-wise trends, or want to create custom filters or dimensions based on specific days.
Example of DAY with Result
DAY(Order Date)
If the Order Date is 2025-06-19, the result will be: 19
Example : 1 Basic Usage
DAY(Signup Date)
Returns the day number of a user’s signup date.
Example 2: Column Usage
Apply the function to an entire column of dates to group or filter data by the day of the month.
Example 3: Handling Decimals and Scientific Notation
The DAY function does not support decimals or scientific notation—it strictly requires a date format.
Example 4: Combining with Other Functions
You can combine with MONTH() or YEAR() for multi-level time analysis:
Tips and Tricks
Combine
DAY()with filters to analyze day-specific data patterns.Create a calculated field:
CASE WHEN DAY(Date) = 1 THEN "First Day" ELSE "Other" END.Use with conditional formatting for visual insights into daily performance trends.
No, the DAY function only works with date-type fields. If your date is in text format, use PARSE_DATE() to convert it before applying the DAY function.
If the input date is null or invalid, the DAY function returns a null result or may trigger an error. Always validate and clean your date fields beforehand.
Yes, DAY works well with functions like MONTH, YEAR, and WEEKDAY. Combining them enables advanced date grouping and in-depth time-based analysis for better insights.
Definitely. DAY helps identify daily behavior patterns or trends that repeat within a month, making it useful for understanding short-term seasonality and campaign performance.
The DAY function adds daily granularity to reports, helping uncover performance patterns, peak activity days, and supporting data-driven decision-making in dashboards and analysis.