There are some things that I think you need to take into account, first is your JOIN, it does not have an ON and looking at the structure of the two tables I do not see a link between them for a JOIN.
Another thing is the lack of a GROUP BY to be clear by which column (I imagine for your exit that is the date) you are grouping items to add up.
I would make the union of two distinct selects (one of revenue and one of expenditure, being that of spending with negative values), would group the result by date and sum all values (how expense is negative in the sum it would subtract
SELECT U.datavencto, SUM(U.valorprogramado)
FROM (
SELECT datavencto, valorprogramado
FROM baixareceita
UNION ALL
SELECT datavencto, valorprogramado * (-1)
FROM baixagasto
) U
GROUP BY U.datavencto
[EDIT]
I put the other fields that you wanted as a return
SELECT U.datavencto, SUM(U.qtd_receber), SUM(U.qtd_pagar), SUM(U.valor_receber), SUM(U.valor_pagar), SUM(U.valor_total)
FROM (
SELECT datavencto, COUNT(idbaixareceita) AS qtd_receber, 0 AS qtd_pagar, SUM(valorprogramado) AS valor_receber, 0 AS valor_pagar, SUM(valorprogramado) AS valor_total
FROM baixareceita
GROUP BY datavencto
UNION ALL
SELECT datavencto, 0 AS qtd_receber, COUNT(idbaixagasto) AS qtd_pagar, 0 AS valor_receber, SUM(valorprogramado) AS valor_pagar, SUM(valorprogramado)*(-1) AS valor_total
FROM baixagasto
GROUP BY datavencto
) U
GROUP BY U.datavencto