Rolling YTD formula using VBA

[automate]

Hi Friends

Request your help regarding :

I would like to know how to have a UDF or custom function to incorporate Rolling forecast formula . A1 to L1 has months like Jan to Dec . A2 to L2 has numbers . I need the formula to be like for Mar it needs to be like April to Dec ( i.e D1 to L1) , and for May its should be from e1 and so on .

thanks in advance
Sankar.R