A better question would be "How often are you worth it?". Some guys get a raw deal ending up with a girl who has little natural sex drive but for the most part, guys that aren't getting it on a daily or at least bi-daily basis have themselves to blame.
I've kept a rule in my house the four years I've been with my fiancee:
You be the same person I met four years ago and I'll do the same
If your life now is leaving dirty socks and dishes around the house, being 20 pounds heavier and looking like a pile of shit most days then its not a shock your wife/gf is far less interested.
This also applies to the fact that if you are a lousy fuck like most men are, then that too gets old after the first six months of a relationship.
Kids do not affect sex, that's a myth, if both parties are into it, it happens, period.
I would suggest looking at yourself first and deciding what you can do to become more sexually appealing to your mate, this can many times be as easy as a surprise dinner or cleaning the house.
I'm a man, I won't settle for less than 5 times a week and there better be a good excuse for why it's even that low. Sex is not just sex, it makes a huge difference in your general life attitude and your life expectancy. It's almost as important as eating.
It takes work like anything else, but if you both can commit to treating your relationship the same today as it was the day you met, (and this can be done) then I promise you a porn star sex life and rock solid relationship.