Hi Nathan

Thanks for posting the sample data and expected results, it doesn't half make a difference. Top work.

Here you go.

;WITH CTEdata AS (

SELECT ExecSeq = ROW_NUMBER() OVER (ORDER BY Dates.[year], Dates.[Month]),

r.Acct_no, r.Amount, Dates.[Month], Dates.[year], i.InterestRate, CAST(0 AS float) AS Interest

FROM (

SELECT [Year], [month]

FROM (

(SELECT TOP 12 [month] = ROW_NUMBER() OVER(ORDER BY [name]) FROM master.sys.columns) m

CROSS JOIN

(SELECT 2007 AS [Year] UNION ALL SELECT 2008 UNION ALL SELECT 2009 UNION ALL SELECT 2010) y

)

WHERE NOT ([Year] = 2010 AND [month] > 2) AND NOT ([Year] = 2007 AND [month] < 8)

) Dates

LEFT JOIN #Refunds r ON r.[year] = Dates.[year] AND r.[Month] = Dates.[Month]

LEFT JOIN #InterestRates i ON i.[year] = Dates.[year] AND i.[Month] = Dates.[Month]),

Calculator AS (

SELECT ExecSeq,

Acct_no,

Amount,

[Month],

[year],

InterestRate,

Interest

FROM CTEdata WHERE ExecSeq = 1

UNION ALL

SELECT cr.ExecSeq,

ISNULL(cr.Acct_no, lr.Acct_no),

ISNULL(cr.Amount, 0),

cr.[Month],

cr.[year],

cr.InterestRate,

Interest = (lr.Amount + lr.Interest) * (1 + (cr.InterestRate/12))

FROM Calculator lr

INNER JOIN CTEdata cr ON cr.ExecSeq = lr.ExecSeq+1

)

SELECT * FROM Calculator ORDER BY ExecSeq