how to perform calculations in sql insert/update statement in postgresql?

example contrived for this example. I have a product table and I need to update the amount column table ( float4 datatype) based on the increment percentage column. 

CREATE TABLE public."Product" (
   id int4 NOT NULL DEFAULT,
   "incrementPercentage" float4 NULL,
   "amount" float4 NULL,
   ...
);

Select allOpen in new window

the incrementPercentage column might have a value or it might be null , so i want to know if the update statement with a case statement will work best. also, would like after I would like to limit the value to 2 decimal places. 

UPDATE Product
SET amount =  CASE WHEN incrementPercentage IS NOT NULL THEN ((incrementPercentage /100)*incrementPercentage  + amount ) ELSE amount END

Select allOpen in new window