This is probably more a plain old .NET question than MM.NET, but MM.NET may have some bearing on it.

I have a Policy which has a date Paid Up To which is a calculated value. What is the best way to implement this so that whenever I refer to oPolicy.PaidTo it always has the latest value?

I guess I need to create the property as part of the BO:

public DateTime PaidToDate = DateTime.MinValue;

(is this the only way to handle null dates?)

and a CalculatePaidTo method as part of the BO which returns a date time value which gets called during construction (or should it get called at some other point?)

Or should I implement this as a Get/Set thing (which I have a very vague idea how to do so I'll probably be back with questions on that).