What does your form controller action look like?

Also please do not calculate prices this way, this will cause floating point rounding errors. Look into using brick/money.

I am assuming the prices and the discount is from the database right? In this case change this code section from

  $presupuestoProducto->discount = ($sale_price * $discount_percentage)/100;

TO

  $presupuestoProducto->discount = ($presupuestoProducto* $presupuestoProducto)/100;

@rvxlab this is my form action:

action="{{ route('presupuestos-productos.store') }}" is this what you mean?

@j-jemoh you mean this to this?

     $presupuestoProducto->discount = ($presupuestoProducto->sale_price* $presupuestoProducto->discount_percentage)/100;