count(*) and limit

I have a interface where users are paging through results of a query. In
order to do so I need to

select count(*) from data where stuff;

To find out how many pages of data there are ( needed for the navigation
bar)

and then I need to

select * from data where stuff limit X offset y;

Now, postgres has to get the whole result before running the limit.

Is there some trick to get how many rows there would be without the limit
so I dont need to run the extra count(*) query? It seems like a waste.

Orion