Ay, that's actually a common question among us, and honestly, safe naman talaga, pero depends kung regular ang cycle mo talaga! If you're trying to avoid pregnancy, mas mababa ang chance sa first day after period, but kung gusto mo ng baby, that's usually not the most fertile window pa (ovulation is usually around mid-cycle for regular cycles). Best talaga to chart your cycle or ask your OB kung ano ang safest approach for your specific situation, kasi every body is different and kami nandito lang may general ideas pero sila ang experts, di ba?