A yuti is a conjunction: two or more grahas in the same sign of your kundli. In the whole sign houses used on this site, sharing a sign means sharing a house, so the grahas act on that house together. Whether a yuti helps or hurts depends on seven things: the sign, the friendship between the grahas, the gap in degrees, combustion, planetary war, the houses they rule, and the aspects on them.
The idea in plain words
Each graha carries its own matters: the Sun the self and authority, the Moon the mind, Mars energy, Mercury speech, Jupiter wisdom, Venus love and comfort, Saturn work and time, Rahu hunger and Ketu detachment. In a yuti those matters blend. A Sun and Mercury yuti, for example, joins the self with the thinking mind, which is why it is called Budhaditya Yoga.
Sanskrit texts use the word yuti or yoga for this meeting. Some named yogas are simply yutis, such as the Moon with Jupiter, which sits inside Gajakesari Yoga, or Jupiter with Rahu, called Guru Chandal.
Step 1: find the sign and each graha's dignity
Write down the sign of the yuti and how each graha stands there: exalted, own sign, friendly, neutral, enemy or debilitated. Take a worked example: Mesh lagna with the Sun at 10°, Mercury at 18° and Venus at 25° of Makar, the 10th house. In Makar, a sign of Saturn, the Sun is in an enemy's sign, while Mercury and Venus are in a friend's sign.
Step 2: check the friendship between the grahas
Natural friendship sets the tone. The Sun counts Mercury as neutral and Venus as an enemy. Mercury counts the Sun and Venus as friends. Venus counts Mercury as a friend and the Sun as an enemy. So in this example Mercury and Venus work well together, and the Sun is the odd one out. The friendship table is the same one used in Kundali Milan.
Step 3: measure the gap in degrees
Grahas within about 10° of each other act strongly on one another. Grahas at opposite ends of a sign, 25° apart, share the house but blend less. In the example, Mercury is 8° from the Sun and Venus 15°. So the Sun and Mercury are close, and Venus sits a little apart.
Step 4: check combustion
A graha too close to the Sun is called asta, or combust, and gives less of its own results. Mercury is combust within 14° of the Sun, or 12° when retrograde, and Venus within 10°, or 8° when retrograde. In the example, Mercury at 8° is combust and Venus at 15° is not. The full table is in Asta Grah.
Step 5: look for planetary war
When two of Mars, Mercury, Jupiter, Venus and Saturn come within one degree of each other, the texts call it graha yuddha, planetary war. The classical texts name a winner by brightness and position, and the loser gives weaker results. The Sun, the Moon and the nodes do not take part. In the example no two grahas are within one degree, so there is no war.
Step 6: read the houses each graha rules
Every graha brings the houses it rules into the yuti. For Mesh lagna, the Sun rules the 5th (children, study), Mercury the 3rd and 6th (effort, rivals) and Venus the 2nd and 7th (money, marriage). All of them meet in the 10th, the house of career. So the example reads as a career built through creative work, communication and partnerships, with the 5th lord's pride needing care.
Step 7: add the aspects
Grahas that aspect the yuti colour it. Jupiter's aspect softens and protects. Saturn's slows and tests. Mars's heats. In the example, if Jupiter sat in the 2nd house, Vrishabh, its 9th aspect would fall on Makar and lift the whole group.
A second worked example: the Moon with Saturn
Take Karkat lagna with the Moon and Saturn together in the 7th house, Makar. The Moon rules the lagna and Saturn rules the 7th and 8th. Saturn is in its own sign and strong. The Moon is in a neutral sign for it, but Saturn treats the Moon as an enemy, so the friendship runs one way. Tradition calls the Moon with Saturn Vish Yoga, a heavy, serious mind.
Put through the seven checks, the yuti reads as a marriage taken very seriously: a partner who is older in manner or in years, slow to show feelings, and steady once committed. The lagna lord sitting with the 7th lord ties the self closely to the partner. If the Moon is within a few degrees of Saturn, the mood of the marriage weighs on the person more. If Jupiter aspects Makar from Vrishabh or Kanya, the heaviness lifts a good deal. The Moon and Saturn pages take this pair through every house.
Where people go wrong
The most common mistake is reading a yuti as a single label, good or bad, without the seven checks. A second is counting grahas that are close in degrees but in different signs as a yuti. In whole sign houses they sit in different houses, though some astrologers still read their closeness. A third is mixing a birth yuti with a transit. A conjunction in your kundli lasts for life, while one in the sky lasts days or weeks, as in our Mangal Shani yuti dates.
Check your own
Open your free kundali, find any house with two or more grahas, and note their signs, degrees and the houses they rule. Then read the matching conjunction page on this site, such as Sun, Mercury and Venus in the 10th house, which takes each house and lagna in turn.