Minimum 18 out of 36 points is necessary by AshtaKoota.
In AshtaKoota (http://www.theastroganesha.com/Articles/matchmaking.aspx) 2 things are necessary:
- No Mangali Dosha. Mangali Dosha is when Ma is located in 1st, 4th, 7th, 8th and 12th only – Lagne 1st Vyaye 12th Chaturthe 4th cha (and), Saptame 7th Ashtame 8th Kujah (Mars/ Mangal/ Kuja). In South India the 2nd house is used additionally (https://en.wikipedia.org/wiki/Mangal_Dosha).
- Friends of both Moon sign lords. If Moon sign lords are not friends, then the friendship of Lagna lords is necessary (https://myjyotish.wordpress.com/basic-information/grahas-planets/).
- Good Nadi (without Nadi Dosha – http://www.kaalsarpyog.com/index.php?option=com_content&view=article&id=47).
- Not many malefic planets should be in the 7th house but some of them is OK (http://1-veda.info/_jyotish/grahas~.html).
- Other AshtaKoota are also taking in account, but it’s not necessary too much to compare with the friendship of Rashi (Moon sign) lords and Nadi Dosha.
- Some other methods:
In compatibility if Rashi lords are not friends, but if Lagna lords are friends then this is OK and you can do marriage.
Note: If a woman has Mangali Dosha and she already have divorce, then her bad effects of Mangali Dosha will not be too strong during her 2nd marriage. Mangali Dosha people also has less negative influence in their 2nd marriage or 3rd marriage compared to the first marriage life because Mangal gives negative influence and same bad effect Shani, Rahu and Ketu but Mangal have more negative influence than Shani, Rahu and Ketu.
If Rahu is influencing 100 % the 7th house but 2nd time (2nd marriage) effects is less – about 75 %.
Guru transit is good in 2nd, 5th, 7th, 9th and 11th house from Moon sign in transit for marriage and also relationship.
Jyotish — “Science of Light” (Vedic Astrology) 