Java loop extracting month and year between two dates
The code would be simpler if you used a Calendar object as the loop variable.

Calendar current = …;
Calendar end = …;

for (; current.before(end); current.add(Calendar.MONTH, 1)) {
    SeguimientoSeccion seccion = new SeguimientoSeccion();
    seccion.setMonth(1 + current.get(Calendar.MONTH));  // natural month number
    seccion.setYear(current.get(Calendar.YEAR));
    secciones.add(seccion);
}


Consider implementing a SeguimientoSeccion.setMonthYear(m, y) method instead, as it's probably useless to set one of the fields without also setting the other.