;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