Just let WCP do all the work , i do, i dont have to think about anything...surely you must of seen this?
Put your suties in, the durations, ie 4 weeks, and itl tell you when to go, tick if youve done or mised them, if they paid or not...debts at the click of a button? Organisation? Accounts? All a click away?
Excel unless your some serious programmer doesnt cut it against WCP mate im sorry