Adding fractional years or months to date

[Krzysztof_Hyla]

Hi, I would like to calculate depreciation end date based on depreciation start date and depreciation duration in years / months. Any idea how to achieve this in Power Query? Here are sample date:

Using Date.AddMonths or Date.AddYears doesn't work with decimal numbers.

[Vijay_A_Verma]

You can use following formula to minimize rounding error to a fraction of a day. 

Date.AddDays(Date.AddMonths([Depreciation Start Date],Number.IntegerDivide([Depreciation Duration in Months],1)),Number.Round(Number.Mod([Depreciation Duration in Months],1)*30,0))

[Krzysztof_Hyla]

Hi Pete, thanks - I have already tried this method. I just hoped there is a solution that doesn't depend on approximation.

[BA_Pete · Accepted solution]

Hi @Krzysztof_Hyla ,

Not sure what you mean by not depending on approximation. If you don't have the actual end date available, how else are you intending to get it without approximating it from the info that you do have available?

You could build the end date from the start date forward which would arguably be more accurate, but you introduce significant complexity for the sake of a day here or there over 3/5/7 years:

let
    __depnMonths = Number.RoundDown([depnMonths]),
    __depnFrac = [depnMonths] - __depnMonths,
    __daysInEndMonth = Date.DaysInMonth(Date.AddMonths([dtDepnStart], __depnMonths)),
    __daysToAdd = Number.Round(__daysInEndMonth * __depnFrac)
in
Date.AddDays(
    Date.AddMonths([dtDepnStart], __depnMonths),
    __daysToAdd
)

Original one-liner versus more complex start-forward build:

Pete

[BA_Pete]

Hi @Krzysztof_Hyla ,

You could try something like this:

Date.AddDays([Depreciation Start Date], 365.25 * [Depreciation Duration in Years])

You may want to round off the days calculation if there's an error with fractional days, something like this:

Date.AddDays(
    [Depreciation Start Date],
    Number.Round(365.25 * [Depreciation Duration in Years])
)

Pete