In SQL how to calculate days in a year based on a start date and the number of days lapsed

What would be the SQL to calculate the number of days in each year if I had a start date and the number of days that have lapsed?

For example, the date (ymd) 2013-01-01 and the days lapsed is 1000.

I would like the result to look like this

2013 = 365

2014 = 365

2015 = 270

Can this be written as a function like datediff?

I have tried using a calendar table, but of course, linking to this just gives me 2013 = 1000

My calendar table looks like this.

DATE_ID  | DATE       | CALENDAR_YEAR | FINANCIAL_YEAR
-----------------------------------------------
20130101 | 2013-01-01 | 2013          | 2013/14

This is what i have tried.

SELECT

D.FISCAL_YEAR, SUM([DAYS]) AS NUMBER_OF_DAYS

FROM [dbo].[FACT] F

LEFT JOIN [dbo].[DIM_DATE] D ON D.DATE_ID = F.DATE_ID

GROUP BY

D.FISCAL_YEAR

The result for this is.

FISCAL_YEAR | NUMBER_OF_DAYS
----------------------------
2013/14     |2820 
2014/15     |6635 
2015/16     |2409

Answer

I would personally build a tally table to do this. Once you build that, you can easly get every date and count the number of days in each year:

DECLARE @YMD date = '20130101',
        @Lapsed int = 1000;

--Build a Tally table
WITH N AS(
    SELECT N
    FROM (VALUES(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL)) N(N)),
Tally AS(
    SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) -1 AS I
    FROM N N1, N N2, N N3, N N4), --10,000 should be enough
--Build the dates table
Dates AS(
    SELECT DATEADD(DAY, T.I, @YMD) AS CalendarDate
    FROM Tally T
    WHERE T.I <= @Lapsed - 1)
--And count the days
SELECT DATEPART(YEAR, CalendarDate) AS Year,
       COUNT(CalendarDate) AS Days
FROM Dates D
GROUP BY DATEPART(YEAR, CalendarDate);

As a function:

CREATE FUNCTION CountDays (@YMD date, @Lapsed int)
RETURNS table 
AS RETURN

    --Build a Tally table
    WITH N AS(
        SELECT N
        FROM (VALUES(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL)) N(N)),
    Tally AS(
        SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) -1 AS I
        FROM N N1, N N2, N N3, N N4), --10,000 should be enough
    --Build the dates table
    Dates AS(
        SELECT DATEADD(DAY, T.I, @YMD) AS CalendarDate
        FROM Tally T
        WHERE T.I <= @Lapsed - 1)
    --And count the days
    SELECT DATEPART(YEAR, CalendarDate) AS Year,
           COUNT(CalendarDate) AS Days
    FROM Dates D
    GROUP BY DATEPART(YEAR, CalendarDate);

GO

SELECT *
FROM (VALUES('20130101',1000),
            ('20150501',755))V(YMD, Lapsed)
     CROSS APPLY dbo.CountDays(V.YMD,V.Lapsed) CD;