if your not wanting to get pregnant, there really is no safe sex time as we dont always ovulate on exactly the same days each month so unless your doing your temps etc you wont know exactly when your ovulating, usually the frist wk after your period is safe, but there are no guarantees, then stay away from sex for the whole of the next wk, then the 3rd wk after your period finishes you should be ok, but you really should be using condoms or another form of birth control if your not wanting to get pregnant :)
First off are you wanting to get pregnant? Your period started on the same day as mine and I just ovulated yesterday. Sperm can only survive 5-7 days if the conditions are right. Meaning you have the proper cervical mucus that is compatible with the semen. You usually only get fertile cervical mucus a few days before ovulation. So the chances of his sperm having survived since the 21st are slim since you said you usually have 29 day cycles. I would have sex tonight if you are wanting to get pregnant because the egg once released can survive 24-48 hrs. If you aren't wanting to get pregnant then wait about 3 days. Hope this is helpful.
if i ovulated from 25th-30th and the sperm lasts for 5 days (which makes it stay inside me until October 26, right?), then there's really a big chance of getting pregnant, right? i'm really confused of how to use the safe period sex.
if you have regular 29 day cycles, you probably will ovulate around the 25-30 october, this is a guide only, and sometimes you can ovulate earlier or later than this, if you did ovulate earlier, then you may get pregnant from the intercourse on the 21st, either way it is too early to tell as implantation take around 7-10 days after fertalisation of the egg, if your trying to get pregnant I would still be having sex as you may not have ovulated yet