How often the two meet
Mars takes about twenty two and a half months to circle the zodiac and Jupiter about twelve years, so Mars laps Jupiter roughly every eight hundred and sixteen days. Their average relative motion is a little under half a degree a day.
At the standard eight degree conjunction orb that gives a window of about five weeks. Compared with a Sun to Jupiter aspect it is twice as wide in time and half as frequent, so the cohort sharing it is larger but rarer.
If Mars turns retrograde inside that window the two can pass, separate and meet again, perfecting up to three times over several months. Someone born during one of those extended passes has the aspect in an unusually emphatic form, and it is the one case where the aspect deserves more attention than the average chart gives it.
Force and scale in the same place
Mars in the tradition is the doing part of the chart: initiative, appetite for conflict, physical effort, the willingness to be the one who starts something. Jupiter is enlargement and confidence, the assumption that more is possible.
A conjunction fuses them, and the fused product is effort at a scale nobody asked for. The older texts read this as courage, physical vigour and a taste for competition, and the modern complaint about it is that the energy is not rationed. Neither body has any interest in restraint, so nothing in the pair itself supplies it.
Where restraint comes from is Saturn, or a strong Mercury, or simply a chart with more earth in it. That is why two people with an identical Mars to Jupiter conjunction can look completely different: one has something in the chart holding the reins and the other does not.
Sign, house and the retrograde question
Sign sets the register. In Aries or Scorpio, Mars is at home and takes the lead in the pairing, which reads as direct and physical. In Cancer or Libra it is uncomfortable, and the same conjunction produces someone who builds up pressure and releases it at odd moments. Jupiter in Sagittarius or Pisces pushes the pair towards belief and travel rather than confrontation.
House needs a birth time and matters more than either. In the sixth this is a working life of long hours. In the ninth it is a life spent moving. In the fourth it is usually described as something that happens inside the family, at a volume the neighbours notice.
Jupiter is retrograde about four months a year and Mars for roughly two months in every two years, so either can be retrograde here. Neither is remarkable, though a Mars retrograde conjunction is the version most likely to have perfected more than once.
How much this actually tells you
Everyone born within the same five week stretch shares the aspect. That is a cohort, not a person, and a page that promises you a specific life from it is selling something. The parts that narrow it to you are the orb, the house and any contact from a third body.
The check above returns the orb. Inside two degrees this is one of the more visible aspects in a chart, generally recognised by the person as their own temperament. Beyond six it is faint, and a tighter Saturn or Mercury contact to the same Mars will outrank it.
If a third planet ties in, read that first. A Saturn square to a Mars and Jupiter conjunction is a much better description of somebody's working life than the conjunction alone, because it explains where the brakes are and what they cost.
Questions people ask about this
How often does Mars conjunct Jupiter?
About every eight hundred and sixteen days, so roughly once every two and a quarter years. At the eight degree orb the aspect holds for around five weeks, which makes it wider in time than a comparable Sun to Jupiter aspect but less frequent.
Can this aspect perfect more than once?
Yes, if Mars turns retrograde while the two are close. The pair can meet, separate and meet again, perfecting up to three times over several months. A chart from one of those extended windows carries the aspect in an unusually strong form.
Is Mars conjunct Jupiter aggressive?
The tradition reads it as vigour and appetite for competition rather than aggression as such. Neither body supplies restraint, so how it shows depends on whether something else in the chart does, usually Saturn or a strongly placed Mercury.
Does the sign change the reading much?
A great deal. Mars in Aries or Scorpio takes the lead and the pair reads as direct and physical. Mars in Cancer or Libra is uncomfortable and the same conjunction tends to store pressure and release it unevenly. Check both dignities before reading the angle.
Does a retrograde Mars or Jupiter matter?
Only mildly. Jupiter is retrograde about four months a year and Mars for around two months every two years, so retrograde placements are common. What a Mars retrograde does signal here is that the conjunction may have perfected more than once.
Do I need a birth time?
For the aspect itself, no, since both bodies move slowly enough that the conjunction is detectable from the date alone. For anything specific, yes. The house placement is what separates your version from everyone else born that month.