In general, someone truly confident that they know the answer to a halachic question is not halachically obligated to seek a ruling.
In many communities, it is nevertheless customary for couples to seek halachic rulings for contraceptive use, regardless of whether they are confident of the answer, because confidence in one’s own knowledge can be misplaced, and because of the gravity of these questions.
In other communities, couples take on more independent halachic responsibility in this area over time, as they build confidence based on prior rulings and discussions.
To learn more about halachic aspects of these decisions and of using particular methods, please see the “Family Planning” section of our site.