The United States Conference of Catholic Bishops offers guidance on the science and methodology of Natural Family Planning at this link.
This includes discussion of four methods of Natural Family Planning:
There are many Catholic ministries with a long track record of success in promoting healthy and faithful marriages. The following are recommended for parishes and marriages in our diocese:
The Choice Wine (https://paradisusdei.org/
Teams of Our Lady (https://www.teamsofourlady.org)
Worldwide Marriage Encounter (www.me.org)
Couples for Christ (https://
Joyful Again (https://joyfulagain.org)
The Christian Family Movement (https://www.cfm.org)
USCCB's For Your Marriage in English & Spanish (https://www.foryourmarriage.