Is it a sin to practice Natural Family Planning with the intent to not have anymore children?

[Teresa_44]

What is the church’s view on no longer wanting to have anymore children?
When I went to a retreat before I got married, we were told NFP could be used to achieve or prevent children…however, it wasn’t until recently that after I had two children, we decided to use NFP for pregnancy prevention and I was then told that was a sin because I vowed to be open to life when I married in the Catholic Church. Of course, if we were to have a surprise pregnancy, no doubt we would raise that child. But is it a sin because we’ve made up our minds to no longer have children?

 

[Fr.Charles_Grondin]

Humanae Vitae:

With regard to physical, economic, psychological and social conditions, responsible parenthood is exercised by those who prudently and generously decide to have more children, and by those who, for serious reasons and with due respect to moral precepts, decide not to have additional children for either a certain or an indefinite period of time.

Responsible parenthood, as we use the term here, has one further essential aspect of paramount importance. It concerns the objective moral order which was established by God, and of which a right conscience is the true interpreter. In a word, the exercise of responsible parenthood requires that husband and wife, keeping a right order of priorities, recognize their own duties toward God, themselves, their families and human society.

…But it is equally true that it is exclusively in the [use of NFP] that husband and wife are ready to abstain from intercourse during the fertile period as often as for reasonable motives the birth of another child is not desirable. And when the infertile period recurs, they use their married intimacy to express their mutual love and safeguard their fidelity toward one another. In doing this they certainly give proof of a true and authentic love.

Moral actions can be sinful for reasons of their inherent nature or the motives for the action. In the case of NFP the action (marital relations outside the fertile period) and omission of action (abstinence during fertile periods) are not inherently immoral. Therefore the morality of the action and inaction falls to the motivation. The above quote from Humanae Vitae shows that there are situations that it is moral to have the motive of avoiding pregnancy.
Only your conscience can truly examine your motives and whether they are truly “serious” and “reasonable.” However, using NFP to indefinitely delay another pregnancy is an not inherently immoral decision.