Generally speaking you are correct:  the date of separation is the date used to value assets in a marriage for purposes of distribution.  But the date of separation can be different for different types of assets and the courts can use different dates for assets that have active contribution from a spouse that contributes to the increase in value or passive contribution.  Although the courts prefer to use a single date they have recognized that maybe multiple dates for different assets are in order.  So they can use a date of  filing legal papers (separation or divorce) or date of trial even. For example, in CA a professional pracitce is valued as of the date of separation to make sure that no income earned in post separation is included in the community estate.  The parties can indeed agree to a date certain or it can be a point of negotiation or litigation.  I would strongly suggest that you have the agreement read by a lawyer if only on a consultation basis.  Good luck.