How Often Is Mercury in the Same Sign as Your Sun?

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Mercury never strays far from the Sun, so your Mercury sign is always your Sun sign or one of the two signs on either side of it. That much is a fixed rule. What the rule does not say is how the three possibilities split. This page counts them, using the same routines as the free chart. For what a Mercury sign is usually read as, see what Mercury signs mean; this page is about frequency only.

The results in brief:

• Mercury was in the Sun's sign on 51.2% of sampled dates, so roughly half.
• It was in the sign just before the Sun's on 24.4%, and in the sign just after on 24.4%. Over the whole sample the two sides balance almost exactly.
• Within one Sun sign they often do not balance. With the Sun in Aries, Mercury was in Pisces on 37.4% of those dates and in Taurus on 15.6%. With the Sun in Virgo the lean reversed.
• Same-sign dates held the most retrograde Mercuries: 25.1% of them, against about 13% on either neighbouring side.
• On 7.3% of local dates the offset did not hold for the whole day, because the Sun or Mercury changed sign at some point between midnight and midnight.

Each figure is a share of dates in one sample. None of them is a share of people.

Calculator note: the free birth chart lists the sign of the Sun and of Mercury in its planet table, but it does not compare the two or mark how many signs apart they are. When the birth time is unknown it checks only the Moon for a possible change of sign during the birth date, not Mercury or the Sun. Ask the Astrologist does not compute these base rates either.

Recap: why only three positions are possible

Seen from Earth, Mercury swings back and forth around the Sun and never gets more than about 28° away from it. A sign is 30° wide, so Mercury can reach the next sign over in either direction but never the one beyond. The degree side of this, including which aspects the Sun and Mercury can and cannot make, is measured on Sun, Mercury and Venus: which aspects are possible.

Here the position is described as an offset, counted in whole signs from the Sun's sign in zodiac order:

• 0: Mercury in the same sign as the Sun.
• −1: Mercury in the sign just before the Sun's. Sun in Aries with Mercury in Pisces is an example; the count wraps round from Pisces to Aries.
• +1: Mercury in the sign just after the Sun's, such as Sun in Aries with Mercury in Taurus.

Sharing a sign is not the same thing as a conjunction. A sign is a fixed 30° slot, while the free chart's conjunction uses an 8° orb that can reach across a sign line. A Sun at 28° Leo and Mercury at 3° Virgo are conjunct but one sign apart; a Sun at 15° Capricorn and Mercury at 4° Capricorn share a sign but are not conjunct.

Sample

The measurement is one offline run of the chart routines behind the free chart, code version 75f5b77, for London (51.5074° N, 0.1278° W) at 12:00 local clock time on each date from 1 January 1920 through 31 December 2059: 51,135 synthetic noon charts. Each sign is read exactly as the routines assign it, and the retrograde marker comes from the same routines. Houses, angles, the Nodes and Chiron play no part. London only fixes the clock-time convention used across the site's other base-rate pages. Noon is the sampling moment, not a guess at anyone's birth time, and dates still ahead are computed positions, not forecasts.

How the three positions split

No date fell outside these three classes.

A same-sign Mercury is the single most common result, but only by a little over half. Close to one chart in two has Mercury in a different sign from the Sun, so a Mercury sign that differs from your Sun sign is an ordinary result, not an exception.

By Sun sign

Each row below uses only the dates on which the Sun was in that sign, so the shares in a row add up to 100% apart from rounding. The number of dates in each row differs a little because the Sun spends slightly longer in some signs than in others.

Two patterns stand out. The same-sign share runs from 46.9% with the Sun in Aries to 58.3% with the Sun in Sagittarius. And the side Mercury leans toward swings through the year: with the Sun anywhere from Capricorn to Taurus it is more often in the sign before the Sun's, from Cancer to Scorpio more often in the sign after, and with the Sun in Gemini or Sagittarius the two sides are level.

These differences reflect the orbital and seasonal geometry of Mercury and the Sun in this sample: how Mercury's path around the Sun lines up with the time of year. They are not a property of Aries, Virgo or any other sign, and they say nothing about people born under them.

Retrograde Mercury by position

The retrograde marker was counted within each offset class, so each figure is a share of the dates in that class, not of all dates.

Over all 51,135 dates Mercury was retrograde on 9,782 (19.1%). The higher share in the same-sign class follows from timing: Mercury turns retrograde around the stretch when it passes between Earth and the Sun, which puts it close to the Sun in the sky. For what the marker is taken to add in a natal reading, see Mercury retrograde in the natal chart.

When the birth time is unknown

A noon chart is one moment. Over a full local birth date the Sun moves about a degree, and Mercury up to about two, so either of them can cross into a new sign before midnight. When that happens, the offset can be different in the morning and in the evening of the same date.

To measure this, each London date was followed through the full local day, from 00:00 up to the next midnight, including the 23-hour and 25-hour days when the clocks change. The day was split at every moment the Sun or Mercury crossed a sign line, located to the minute, and the offset was checked in each piece.

• 3,717 of the 51,135 dates (7.3%) had more than one offset during the day. On the other 92.7% a noon chart gives the right offset whatever the birth time.
• The four possible one-step changes were about equally common: 0 to +1 and +1 to 0 on 942 and 941 dates, 0 to −1 and −1 to 0 on 937 dates each.
• On 34 dates the offset changed and then changed back before midnight, for instance when Mercury moved into the next sign first and the Sun followed it there later the same day. Comparing only the start and end of the day would miss these.
• On 6 dates three offsets occurred in one day, each time running from +1 through 0 to −1.

If you do not know your birth time and your Sun or Mercury sits within a degree or two of a sign line, the offset may be uncertain for that date. Checking only the beginning and end of the day is not enough, because, as the 34 dates above show, the offset can change and change back in between. What matters is whether the offset changes at any point during the full local calendar day, and the free chart does not run that full-day check for Mercury. So with an unknown time, treat a near-boundary case as possibly uncertain rather than assuming the noon chart or the two ends of the day settle it. The guide to a chart without a birth time explains why noon is used as the default.

Ruben as the worked example

Ruben is the fictional chart from how to find aspect patterns: London, 5 January 1993, 12:00. He was fixed as the example before any figure on this page was calculated.

• Offset 0. Mercury is in the Sun's sign, the most common of the three classes and the one shared by 57.0% of the sampled Capricorn dates.
• Same sign, not conjunct. The two are 10.75° apart, outside the 8° conjunction orb, so his chart has no Sun-Mercury conjunction even though both are in Capricorn.
• Direct. His Mercury carries no retrograde marker.
• The same all day. The Sun at 15° and Mercury at 4° of Capricorn are both well clear of a sign line, so his offset is 0 at every time on 5 January 1993.

His result is common, which is all it shows. It does not make his Mercury more typical in meaning, only in position.

Reading the base rate sensibly

Knowing where your Mercury falls among these classes says how common the arrangement is, nothing more. A Mercury in a different sign from the Sun is not a mismatch or a flaw, and a shared sign is not a strength. Nothing here describes intelligence, behaviour, health, relationships, money or future events.

Doing the check yourself

1. Read the signs of the Sun and Mercury from the planet table of the free birth chart.
2. Count in zodiac order from the Sun's sign to Mercury's: same sign is 0, the sign before is −1, the sign after is +1.
3. Compare with the row for your Sun sign above.
4. With an unknown birth time, check whether the Sun or Mercury is near a sign line. If either is, treat the offset as possibly uncertain for that date; the start and end of the day alone cannot confirm it.
5. For the same question about Venus, which has five possible positions instead of three, see how often Venus is in your Sun sign.

Related articles

• How Often Is Venus in the Same Sign as Your Sun?
• What Mercury Signs Mean
• Sun, Mercury and Venus: Which Aspects Are Actually Possible?
• Sun Conjunct Mercury
• Mercury Retrograde in the Natal Chart
• How Long Does Each Planet Stay in a Sign?