Two planets that travel together
Budha is Mercury, the planet of intellect, speech and trade, and Aditya is a name of the Sun, the planet of the self and authority. Budhaditya yoga is their meeting in one sign. Mercury is never more than about 28 degrees from the Sun as seen from Earth, so the two share a sign in a large share of charts. The tradition reads the pairing as a sharp, articulate mind that is applied to practical ends. It is a pleasant reading and a fair one, but the yoga is common, and it is the details that make it individual.
How the finder checks it
You give your date, time and place of birth. The tool works out the sidereal positions of the Sun and Mercury (Lahiri ayanamsa) and asks the yoga engine behind the Yoga Analysis panel of the free kundali whether they share a sign. If they do, the result shows the sign, the house it falls in, and the exact separation in degrees. It also checks the conditions that classical teachers connect with the strength of the yoga: whether Mercury is combust, whether either planet is debilitated or in the 6th, 8th or 12th house, and whether a node is in the same sign.
If the two planets are in different signs the finder says so, with the signs, and that is all there is to it. Many people have a sharp mind and a fluent tongue without this yoga.
What the degree gap tells you
Combustion is the central question for this yoga. A planet that is very close to the Sun is said to be burnt by its light, and a combust Mercury is read as having less independence. Orbs differ between authors, and the finder uses the common values, with a smaller orb when Mercury is retrograde. A Mercury a good distance from the Sun, say more than ten degrees, is read as stronger than one that is nearly exact. Teachers who take this view say the yoga is at its best when Mercury is clear of the Sun but still in the same sign.
Other teachers argue that the yoga is simply the conjunction and that combustion is a separate matter. This finder reports both facts, so you can follow whichever school you prefer. The house matters too. The pair in the 10th house is read as an intellect in public work, in the 2nd as a gift for speech and accounts, and in the 5th as a studious mind. These are tendencies, and the sign decides much of the colouring. A pair in Gemini or Virgo, the signs ruled by Mercury, is at ease, and the same pair in Pisces, where Mercury is debilitated, is read with caution.
Reading it with the rest of the chart
The yoga speaks most in the dashas of the Sun and Mercury and in the transits that touch them. The Sun’s sign in your chart is worth reading in the sun sign guides, and the planets’ houses are explained in the house lords guide. The Mahadasha calculator shows when the Sun and Mercury periods fall for you. Do not treat the yoga as proof of talent: it names a tendency, and talent is built.
About the rule
The rule used here is the plain one, the Sun and Mercury in one sign, the way the engine applies it. Some authors ask for the two to be within a certain number of degrees, and others want the pair in a particular house, so another tool may report a different result. Read the guide to Budhaditya yoga for the classical background and the common variations.
Frequently asked questions
↳ Is Budhaditya yoga rare?
No. Mercury stays within about 28 degrees of the Sun, so the two often share a sign. The yoga is common, and its value depends on the sign, the house and how close Mercury is to the Sun.
↳ Does combustion cancel the yoga?
Many teachers say a combust Mercury reduces it, though some hold that the conjunction alone makes the yoga. The finder reports the degree gap and the combustion so that you can read it either way.
↳ Does it make me intelligent?
The tradition reads it as a tendency towards an alert, practical mind. It is not a measure of ability, and many people without it are highly capable.
↳ Which sign is best for the pair?
Mercury is comfortable in Gemini and Virgo, and the Sun in Leo and Aries. Teachers read the pair with caution in Pisces and Libra, where Mercury or the Sun is debilitated.