Expanding sum based on months

Hi,

I'm trying to set up a variance anaylsis spreadsheet which has both the current month (which I have sorted) and the YTD figures.

I want to be able to do the YTD figure sum based on Jan to current month.
For instance if the Variance spreadsheet shows that the current month is 3 (March), then the YTD figure needs to sum the figures from January to March.

Hope that's explanatory enough.

Cheers

Matt