Gaj Kesari Yog is formed in any horoscope when Jupiter is in Kendra from Moon which means when Jupiter is in house number 1, 4, 7 or 10 from Moon. This Yog can bless the native with great fame, great skills, success, wealth and many other things. Now as we know that there are only 12 houses in a horoscope and Jupiter can be present in any one of these 12 houses, when we count from the house of placement of Moon, the presence of Jupiter in 4 out of 12 houses will lead to the formation of Gaj Kesari Yog in the horoscope which means that randomly, every third person is having a Gaj Kesari Yog in his horoscope since there are only 12 houses in a horoscope and the probability of Jupiter being placed in any one of 4 specific house out of 12 houses is one third. Analyzing this definition further, we know that Moon transits a sign for 2 and a half days approximately and since the formation of Gaj Kesari Yog is decided by the placement of Jupiter from Moon, a Gaj Kesari Yog once formed stays active for about 2 and a half days which means that all the people born all around the world during these 2 and a half days will have a Gaj Kesari Yog in their horoscope. To simplify this fact, let us assume that Jupiter is present in Aries at a time and as we know that Jupiter stays in a sign for about a year, so when Moon enters in any of the signs namely Aries, Cancer, Libra or Capricorn, a Gaj Kesari Yog will be formed as Jupiter will be in house 1, 10, 7 and 4 from Moon in these cases. Since Moon stays in a sign for 2 and a half days and Jupiter does not change its sign fast, it means that a Gaj Kesari Yog will be active continuously for 2 and a half days.
The fact that a Gaj Kesari Yog is found in almost every third horoscope and the fact that this Yog remains activated for about 2 and a half days are very hard to justify practically as the good results associated with Gaj Kesari Yog are not so common which can be found in every third person and any one of a very good Yoga in Vedic astrology does not remain activated continuously even for an hour, let alone 2 and a half days. This means that there are more conditions for the formation of Gaj Kesari Yog in a horoscope than the one mentioned in prevalent definition of this yog and we will now discuss about these conditions. To start with, both Jupiter and Moon should be working benefic in the horoscope for the formation of a Gaj Kesari Yog in the horoscope and if anyone or both of these planets are working malefic in a horoscope, a Gaj Kesari Yog will not be formed in the horoscope and the malefic planet will afflict the benefic planet which will cause problems instead of benefits. For example, if Moon and Jupiter are present in the same house of a horoscope, Moon is banefic but Jupiter is malefic, a Gaj Kesari Yog will not be formed in this case but this combination of a malefic Jupiter with a banefic Moon will bring problems which will revolve around the significances of Moon. The worst kind of combination can happen when both Moon and Jupiter are working malefic in a horoscope as in this case, both the planets will suffer from the malefic effect of the other planet and no Gaj Kesari Yog will be formed in the horoscope.
And even when a Gaj Kesari Yog is actually formed in the horoscope, its results will not be the same for different natives and they will change considerably according to the horoscopes of these natives. For example, a Gaj Kesari Yog formed due to the presence of a benefic Jupiter and Moon in Cancer sign is generally much stronger than a Gaj Kesari Yog formed due to the presence of a benefic Jupiter and Moon in Scorpio or Capricorn as Moon and Jupiter respectively are debilitated in these signs and hence they cannot contribute much towards this yog. Similarly a Gaj Kesari Yog formed due to presence of a benefic Jupiter and Moon in the same house is likely to be stronger than the Gaj Kesari Yog formed due to presence of benefic Jupiter in 7th house from Moon which is in turn stronger than the one formed with benefic Jupiter in 4th house from Moon which is stronger than the Gaj Kesari Yog formed with Jupiter in 10th house from Moon. The impact of other positive and negative planets on Jupiter, Moon and Gaj Kesari Yog itself should also be analyzed as this impact can considerably increase or decrease the strength of this yog. The placement of Jupiter and Moon in different signs and different house of a horoscope can also make a great difference in net resultant of Gaj Kesari Yog and the overall tone of the horoscope should also be checked properly before predicting the good effects of Gaj Kesari Yog in a horoscope.