Originally Posted by yancydc
I'm not familiar with those kits, but are they partial boils, i.e. you add water after the boil? It's common for the OG to be off due to the top up water not mixing completely.
I agree, give the carboy a good swirl/mix before sampling it for OG. Also make sure it's at the correct cooled temperature if using a hydrometer.
There are methods of calculating expected gravity from the #s of extract added per gallon of beer (5gal). Reference "how to Brew" by Strong. Too lazy to write it here. :P