Can I make a custom function like DatesYTD and DatesMTD ?

[mds123]

My data needs to be reported at a period level and a period is roughly 28 days, but not always. I need to report the cumulative sales at the day level for each period. The dax functions DATESMTD and DATESYTD are able to provide a cumulative sales at the month and year level. Are there any ways I could do this at the period level? Am I able to see the underlying code for those functions and make my own?

I can use calculate([Total Sales], DATESMTD(Dates[Date])) to get the cumulative sales for the month, but I need to get it at the period level.

My dates table is designed below. 

Date | Period | Fiscal Year

[mh2587]

First Create date period table like following:
| PeriodID | StartDate   | EndDate     |
|----------|-------------|-------------|
| 1        | 2024-01-01  | 2024-01-28  |
| 2        | 2024-01-29  | 2024-02-25  |
| 3        | 2024-02-26  | 2024-03-24  |
| ...      | ...         | ...         |

//And then use this measure 

CumulativeSalesPeriod = 
CALCULATE(
    SUM('YourTable'[Total Sales]),
    FILTER(
        ALL('YourTable'[Date]),
        'YourTable'[Date] <= MAX('YourTable'[Date]) &&
        'YourTable'[Date] >= MIN('YourTable'[Date]) &&
        'YourTable'[Date] >= RELATED('PeriodTable'[StartDate]) &&
        'YourTable'[Date] <= RELATED('PeriodTable'[EndDate])
    )
)

[Greg_Deckler]

@mds123 You may find this helpful - https://community.powerbi.com/t5/Community-Blog/To-bleep-With-Time-Intelligence/ba-p/1260000

Also, see if my Time Intelligence the Hard Way provides a different way of accomplishing what you are going for.

https://community.powerbi.com/t5/Quick-Measures-Gallery/Time-Intelligence-quot-The-Hard-Way-quot-TIT...