If my blood test taken 12days af yer the missed period for bhcg came as 0.4 & home pregnancy test also negative. can i be sure i am not pregnant.

Home pregnancy tests are very accurate.: They are the same tests used in a doctors office. They can detect a pregnancy 7-10 days after conception. The best time to take one is when you miss your period.  if you doubt the result you can repeat it in 1-2 days. If you were pregnant the hormone level would rise enough for detection.

BHCG: May be? As you said home pregnancy test in negative- but given the fact that it could be false negative, serum beta HCG would be doubled every 48-72hrs in pregnancy. You said 0.4 (units?). I dont know what do you mean by that, also dont know what is your lmp, but HCG level below 5 miu/ml is considered "not pregnant. Final recommendation: you can repeat test in few days, as there is less info.