If you believe in the Bible then you know that the soul enters the body with the first breath. A fetus does not have a soul, so the time in the womb doesn't count.

Besides, 'birthday' literally means the day you were born.

So $10 × 52 weeks = $520 annually. $520 ÷12 = $43.33 per month. $520 ÷ 365 = $1.43 per day.

Estimates are more accurate by figuring annually first, then dividing by the smaller units.