sub select as a data column

I am having trouble coming up with words to describe exactly what I need so
searching for a solution is getting frustrating! If this has been answered
twelve hundred times - please forgive me!

I want to do in postgresql what I do in oracle:

select year report_year,
sum(amount),
sum(select amount from my_table where year <= report_year)
from my_table
group by report_year;

I see lots of stuff on subselect in the from clause - but how do you
subselect as a data column?

Thanks for the help - it is SEVERLY appreciated!
Ronni