Need Help in Formula IF(A1=A2,AC1,AB2)

No.

' in #"Added Custom" ' is nothing to do with the calculation at all, it's just a marker so Power query knows which step to show as the final table.

Select your #"Added Index" step in the query list, then just add this as a new custom column:

try
if [Document Id] = #"Added Index"[Document Id]{[Index] + 1} then [#"Actual End Date & Time"] else #"Added Index"[#"Actual Start Date & Time"]{[Index] + 1}
otherwise null

Power Query will sort out all the other references for you.

Pete

Hi Pete,

I tried the mention below code 

= Table.AddColumn(#"Added Index", "Custom", each
try
if [Document Id] = #"Added Index"[Document Id]{[Index] + 1}
then [Actual End Date of Process]
else #"Added Index"[Actual Start Date of Process]{[Index] + 1}
otherwise null
)in #"Added Custom"

Got this error. Can you please check and help

It looks like you just need to put the ' in #"Added Custom" ' bit on the next row, rather than right after the last bracket.

Pete

Like this 

= Table.AddColumn(#"Added Index", "Custom", each
try
if [Document Id] = #"Added Index"[Document Id]{[Index] + 1}
then [Actual End Date of Process]
else #"Added Index"[Actual Start Date of Process]{[Index] + 1}
otherwise null
in #"Added Custom")

Hi Dear,

Added the same code 

= Table.AddColumn(#"Added Index", "Custom", each
try
if [Document Id] = #"Added Index"[Document Id]{[Index] + 1}
then [Actual End Date of Process]
else #"Added Index"[Actual Start Date of Process]{[Index] + 1}
otherwise null
in #"Added Custom")

and got error 

My table name is InvoiceLife_Cycle and mention below the the table structure and I want to get the new date into new colunm name start date. I am new to power bi so please help me in detail.

this is my table

Hi Pete,

Solution gives me correct data but ufortunately when click applied and closed andit will increase the size of table to 1000 times. Can you please suggest why it happen

What do you mean it increases the size of the table 1,000 times? Are you getting duplicated rows or are you talking about application rows as it loads?

Pete

my sheet file size is 15MB and after adding this custom column when i click on close and apply button power bi load shows size more than 3 GB and it keeps on loading not able to save the changes in the table.

Ok. It sounds as though PQ is rescanning everything multiple times.

In your query, insert a step after #"Added Index" like this:

bufferStep = Table.Buffer(#"Added Index")

Then adjust your calculation step to this:

try
if [Document Id] = bufferStep[Document Id]{[Index] + 1} then [#"Actual End Date & Time"] else bufferStep[#"Actual Start Date & Time"]{[Index] + 1}
otherwise null

Note that I've updated the step references to point to the buffered table. This should prevent PQ having to constantly reload the same table for scans.

Pete