[marcoszorrilla]

Esta es la función en D5:

Código Delphi [-]
function Payment(Rate: Extended; NPeriods: Integer; PresentValue, FutureValue:
  Extended; PaymentTime: TPaymentTime): Extended;
var
  Annuity, CompoundRN: Extended;
begin
  if Rate <= -1.0 then ArgError('Payment');
  Annuity := Annuity2(Rate, NPeriods, PaymentTime, CompoundRN);
  if CompoundRN > 1.0E16 then
    Payment := -PresentValue * Rate / (1 + Integer(PaymentTime) * Rate)
  else
    Payment := (-PresentValue * CompoundRN - FutureValue) / Annuity
end;

Un Saludo.