Formula with a value of the last record

First of all excuse me for my poor english.

Let's se if I make any sense. I have a field of total in a record of a day and want that same field start as a balance on the next day 

i tried to use this formula: 

let myRec := this;
let prevDate := max((select Caixa)[Dia < myRec.Dia].Dia);
if prevDate then
    let prevRec := first((select Caixa)[Dia = prevDate]);
    prevRec.Saldo
end

but after safe occurs an error of "circular reference"

if someone coud help me