How is Last Cost calculated?

The last cost for a product is determined by the most recent cost establishing transaction that took place in a particular warehouse.

The last cost for a product is determined by the most recent cost establishing transaction that took place in a particular warehouse.  These transactions are receipts, assemblies, and transfers that add value.  Transfers out of that warehouse, for example, wouldn't update the last cost.  Other transactions such as adjustments, issues, an balance adjustments are excluded as well.

LastCost

Only products with an inventory type of "Inventoried" or "Special order only" can have a last cost since other product types aren't kept within inventory.  If you wish, it's also possible to manually override the last cost in edit mode and enter the value you want into the last cost field.  This can be useful if utilizing prices that calculate based on last cost.  However, keep in mind that the next transaction that takes place will cause Acctivate to recalculate costing and update the field once again.