How often should newly couple have sex for pregnancy?

It depends on many factors. If both people are young and healthy then having sex when they feel like it works as well as (and sometimes better than) timed sex. This is because women naturally feel more inclined to have sex when they are most fertile. Nature also makes women appear most attractive when they are most fertile so if a couple respond to their natural sexual desires pregnancy should follow within a few months.

If you really want to time sex then the best time depends on the length of the woman's menstrual cycle. The average cycle is 28 days. ovulation happens 10-14 days BEFORE menstruation so ovulation happens on one day between days 14 and 18. This means sex after day 18 is useless. Sex between day 10 and 18 could result in pregnancy. If the man's sperm count is normal then once daily sex is fine. If his sperm count is low then sex every second day is preferred to give his body time to make sufficient sperm.

Of course the woman's menstrual cycle might be shorter or longer than 28 days. There are also ways for a woman to track ovulation by noticing changes in her body.

Paying too much attention to these things and becoming stressed about it can actually decrease the chances of pregnancy. If both people are healthy then having sex every 2-3 days when the woman's menstruation has ended until just after the middle of her cycle should work just fine - particularly if attention is paid to when she is feeling most interested in sex!