IfSum question

[ACoffi1967]

I have an Excel sheet with 12 columns and several rows of data.  I need to create a column of YTD information that will change depending upon the month.  What would my formula be if I change the # in the current month cell "O" so that my ytd # becomes the sum of all the months to that point?

												Current Month	4
Description	Month 1	Month 2	Month 3	Month 4	Month 5	Month 6	Month 7	Month 8	Month 9	Month 10	Month 11	Month 12		YTD
Revenue	100	200	300	400	500	600	700	800	800	800	800	800
COGS	50	50	50	50	50	50	50	50	50	50	50	50
Gross Income	50	150	250	350	450	550	650	750	750	750	750	750

[#2]

@ACoffi1967 In what would be P3 (if I counted correctly) enter this:

=SUM(C3:OFFSET(B3,0,$O$1))

[#3]

Revenue is Row 3, Description is Column A = so revenue is A3
For each month then Revenue would be B3, C3, etc.
The # that changes o return the sum is Current month - in example 4 in Cell N1
So if N1 is 4 the total should be sum of B2:E2
If N1 changes to 3 the total should be sume of B2:D2

[#4]

Got it! Thanks.