If you are using an accounting package, it should do it automatically. The PNL shows the profit and loss from the balance carried forward. And YEP, 2013 starts with the balance carried forward from 2012.

SO, if 2012 started with $1000, and you made $3000, the balance in 2013 starts with $4000. If it ends with $8000, you made a $4000 profit(8000-4000). of course that IS an oversimplification as the money could come from anywhere, but you get the point.

Basically, everything is like a set of running balances. If not for the fact that you have recurring events, and agencies want fixed snapshots, etc.... You would probably never have monthly, quarterly, yearly views.

Steve