Calculate New Column in sql server

Question

CREATE TABLE [dbo].[Table1](
    [Months] [int] ,
    [AccumSD] [decimal](38, 2)
GO
insert into [Table1]([Months],[AccumSD])
select 1    ,0.00
Union All
select 2    ,21574680.03
Union All
select 3    ,16706196.47
Union All
select 4    ,-7873127.29
Union All
select 5    ,-4235468.46
Union All
select 6    ,-2201146.63
Union All
select 7    ,-2102177.16
Union All
select 8    ,-315589.57
Union All
select 9    ,1638011.39
Union All
select 10    ,1826178.79
Union All
select 11    ,1883942.48
Union All
select 12    ,1585631.16
The above is the table structure and data.
I want to calculate the column from AccumSD + previous value of same column (AccumSD)
the calculated column should be like the below
0
21574680.03 
16706196.48 
13701552.75 
12470728.02 
11500406.13 
10368550.87 
11184816.56 
12006562.26 
13010995.35 
13890504.74 
14596626.51 
15540690.5 
16386422.24 
17231803.58 
18101710.92 
18971480.26 
19910089.6 
26235684.8 
32481280 
How can we achieve it? Thanks in advance

Answer 1

The formula from your excel screen grab does not match the formula you posted in your description.
Your example data does not match your screen grab.
Best of luck getting to an answer that works for you.
Agreed. While the OP may regard his maths to be good and his sample data spot on, it leaves their eyes as I fail to see how their data matches what they appear to be asking for.
OP, your first three rows are
select 1   
,0.00
select 2   
,21574680.03
select 3   
,16706196.47
How does that lead to
Select @A= 0 + 0
Select @A
 Select  @A=21574680 +@A
Select @A
 Select  @A= -4868484 + @A
Select @A
Where did "-4868484" come from?
Unless you give accurate requirements, how can anyone help you? Looking at your excel screenshot, you are negating, not summing.