Quick Answer
The correct answer is DATESINPERIOD, as this DAX function is specifically designed to calculate a running total over a dynamic window of time, such as a rolling 12 months. By using DATESINPERIOD with CALCULATE, you define a date range that shifts backward from the last date in the current filter context—for example, CALCULATE(SUM(Sales[Amount]), DATESINPERIOD('Date'[Date], MAX('Date'[Date]), -12, MONTH))—which automatically updates as new data is added. On the PL-300 exam, this tests your understanding of time intelligence functions and the requirement that a 'Date' table be marked as a date table for these functions to work correctly. A common trap is confusing DATESINPERIOD with DATESBETWEEN or TOTALYTD; remember that DATESINPERIOD is the only one that lets you specify a negative interval to go backward from a reference date. Memory tip: think “DATESINPERIOD = dynamic period in the past,” and the negative number tells it to roll backward.
This PL-300 practice question tests your understanding of model the data. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You have a Power BI model with a 'Date' table marked as a date table. You need to create a measure that calculates the running total of sales over the last 12 months. Which DAX function should you use?
PREVIOUSYEAR
Why wrong: PREVIOUSYEAR returns the entire previous year.
DATESYTD
Why wrong: DATESYTD calculates from start of year to current date, not last 12 months.
DATESINPERIOD
DATESINPERIOD can return a set of dates going back 12 months from the current date.
DATEADD
Why wrong: DATEADD shifts dates but does not directly create a rolling period.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
DATESINPERIOD
Option C, DATESINPERIOD, is correct because it allows you to define a dynamic window of dates—specifically, the last 12 months ending with the latest date in the current filter context. When used with a measure like CALCULATE(SUM(Sales[Amount]), DATESINPERIOD('Date'[Date], MAX('Date'[Date]), -12, MONTH)), it shifts the date range backward by 12 months from the last visible date, making it ideal for a rolling 12-month total. The 'Date' table being marked as a date table ensures that time intelligence functions respect the continuous date range.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
PREVIOUSYEAR
Why it's wrong here
PREVIOUSYEAR returns the entire previous year.
DATESYTD
Why it's wrong here
DATESYTD calculates from start of year to current date, not last 12 months.
DATESINPERIOD
Why this is correct
DATESINPERIOD can return a set of dates going back 12 months from the current date.
Related concept
Read the scenario before looking for a memorised answer.
DATEADD
Why it's wrong here
DATEADD shifts dates but does not directly create a rolling period.
Common exam traps
The trap here is that candidates often confuse DATESYTD (which is for year-to-date, not rolling) with a trailing 12-month calculation, or they mistakenly think PREVIOUSYEAR can handle a dynamic window, when in fact it only returns a fixed prior calendar year.
Detailed technical explanation
DATESINPERIOD works by generating a contiguous range of dates from a start date (specified by the second argument) backward or forward by the given interval, which is essential for rolling calculations like trailing 12 months. Under the hood, it leverages the 'Date' table's continuous date column and respects the marked date table's calendar boundaries, ensuring no gaps or partial periods. A subtle behavior is that if the current filter context has no single last date (e.g., multiple months selected), you must use MAX('Date'[Date]) to get the latest date in context; otherwise, the measure may return unexpected results.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
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FAQ
Model the data — This question tests Model the data — Read the scenario before looking for a memorised answer..
The correct answer is: DATESINPERIOD — Option C, DATESINPERIOD, is correct because it allows you to define a dynamic window of dates—specifically, the last 12 months ending with the latest date in the current filter context. When used with a measure like CALCULATE(SUM(Sales[Amount]), DATESINPERIOD('Date'[Date], MAX('Date'[Date]), -12, MONTH)), it shifts the date range backward by 12 months from the last visible date, making it ideal for a rolling 12-month total. The 'Date' table being marked as a date table ensures that time intelligence functions respect the continuous date range.
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Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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