Cancer and Libra compatibility has a quiet twist. Mars is the planet of anger, drive and the push to get what you want. The old books call Mars weak in Cancer. They call it weak in Libra too. So this couple is built from two signs where the fighting planet is out of its depth.
That is the thread of this page. I counted how common the pair is in US births. About 1 random US couple in 66 is a Cancer with a Libra. Then I counted real charts. In about 2 of these couples out of 5, at least one partner has Mars in Cancer or in Libra. Each number comes with its method, so you can check it.
The short answer, in six lines
| Question | What I found. |
|---|---|
| How common is a Cancer and Libra couple? | About 1 random US couple in 66, or 1.51 percent. |
| Where does it rank among the 78 pairs? | Ninth, and second among the squares. |
| How far apart are the signs? | Three signs, or 90 degrees, a link called a square. |
| What do the old books say about Mars here? | It is in its fall in Cancer and in exile in Libra. |
| How many couples carry that weak Mars? | About 2 in 5, in at least one of the two charts. |
| Did real marriages favor or avoid the pair? | No. The count came within one percent of chance. |
First, what no one can promise
Astrology is not a science. No study has shown that a Sun sign predicts how a couple will do. The largest test I know of was run by David Voas, then at the University of Manchester, in 2007. He used the 2001 census of England and Wales. It holds the birth dates of more than 10 million married couples.
He asked a plain question. Do some sign pairs marry more than chance allows? His answer was no. He also found why some raw counts looked odd. Too many couples shared a sign, because a clerk or a spouse wrote the same birthday twice. Once he took out those errors, the table looked random. The Skeptical Inquirer reported his result in March 2008.
Here are the Cancer and Libra cells from his corrected table, Table 7. It holds 9.5 million couples.
| Couple in the 2001 census | Found | Expected by chance | Gap. |
|---|---|---|---|
| Cancer wife, Libra husband. | 65,032 couples. | 65,501 couples. | 469 fewer. |
| Libra wife, Cancer husband. | 65,918 couples. | 66,113 couples. | 195 fewer. |
| Both kinds together. | 130,950 couples. | 131,614 couples. | Half a percent fewer. |
The expected count is what you get if people pick partners with no regard to sign. Voas notes that a cell can drift up to 450 from that count by pure chance. The first cell sits just past that line. He lists a scatter of such cells, from 680 below to 631 above. He adds that the biggest gap in all 144 cells is barely 1 percent. With a sample this large, he says, such gaps carry no real meaning.
So Cancers and Libras do not seek each other out, and they do not avoid each other. This page reads the pair as a lens, not a forecast. The lens gives two people words for how each one works. The two people decide the rest.
How common is a Cancer and Libra couple?
Your Sun sign is the slice of the sky the Sun stood in when you were born. There are twelve slices of 30 degrees each. Cancer season runs from about June 21 to July 22. Libra season runs from about September 23 to October 22.
The signs are not equal in births. Two things set the count. The first is how long the Sun stays in each sign. The second is how many babies are born per day in that part of the year. Cancer wins on both. The Sun spends about 31.45 days in Cancer, the longest stay of the twelve. US births climb through the summer. Libra gets about 30.4 days, in a month when births start to slow.
I counted it with two public files of daily US births.
| Question | Social Security file, 2000 to 2014 | Health Statistics file, 1994 to 2003. |
|---|---|---|
| Births in the file. | 62.2 million births. | 39.7 million births. |
| Share born with the Sun in Cancer. | 8.84 percent, third of twelve. | 8.87 percent, third of twelve. |
| Share born with the Sun in Libra. | 8.52 percent, fifth of twelve. | 8.51 percent, fifth of twelve. |
| Chance a random pair is one Cancer and one Libra. | 1.51 percent, or 1 pair in 66. | 1.51 percent, or 1 pair in 66. |
Why multiply by two? A couple can be a Cancer woman with a Libra man, or the other way round. Both count. So the chance is two times the Cancer share times the Libra share. If every sign held one twelfth of births, the pair would show up once in 72 draws. It shows up once in 66.
There are 78 ways to pair the twelve signs, same sign pairs included. Cancer and Libra come ninth. Among the twelve pairs of signs set three apart, only Gemini and Virgo is more common, at 1 in 65. The rarest of those twelve is Aries and Capricorn, at 1 in 80.
None of this comes from the stars. It comes from the calendar and from the months when US babies are born. A common pair is not a better pair. It is a pair you are more likely to meet.
Three signs apart: the square
Place the twelve signs on a wheel. Count from Cancer: Leo, Virgo, Libra. That is three steps, or 90 degrees. Astrologers call this link a square. An aspect is a set angle between two points in the sky, and the square is one of the four that Ptolemy names.
Why the old books call it hard
Claudius Ptolemy wrote the Tetrabiblos in Alexandria around 150 AD. It is the oldest full textbook of Western astrology. I read Book 1 in the English version by Frank Robbins, from 1940. In chapter 13 he sorts the aspects. The trine and the sextile join signs of the same kind, so he calls them harmonious. The square and the opposition join signs of opposite kinds, so he calls them disharmonious.
The kinds are male and female, and they take turns around the wheel. Cancer is a female sign. Libra is a male sign. So here his reason fits. The pair joins two signs of opposite kinds, which is what he means by a hard link.
A true square needs birthdays about 93 days apart
A sign is a slice, so the label does not fix the angle. For an exact square, both Suns must sit at the same degree of their signs. I timed the Sun from each degree of Cancer to the same degree of Libra, for every year from 1990 to 2030. The trip takes between 92.6 and 93.7 days.
That is a bit more than a quarter of a year. The Sun moves slowest in early July, when Earth is farthest from it. So the summer quarter runs long. Here is a real example. In 2026, the Sun reached 15 degrees of Cancer on July 6 at 9:57 p.m., New York time. It reached 15 degrees of Libra on October 8 at 2:30 a.m., New York time. A Cancer born on July 6 and a Libra born on October 8 of that year have their Suns in an exact square.
How many pairs have a true square
An early Cancer and a late Libra have Suns about 120 degrees apart. A late Cancer and an early Libra are about 60 degrees apart. The label says 90, but the real gap runs from about 60 to 120 degrees.
Astrologers count an aspect only when the angle is close to exact. The leeway they allow is called the orb. Our pages on other pairs weighed each degree by real US births. They found the same shares for every pair of signs: about 19 percent within 3 degrees, 36 percent within 6, 46 percent within 8, and 56 percent within 10. The width of a sign sets those shares, not the pair. So with a 6 degree orb, only about 1 Cancer and Libra couple in 3 has Suns in a true square.
A solstice sign and an equinox sign
In chapter 11, Ptolemy names four signs that start a season. Cancer begins at the June solstice, the day the Sun stops climbing north and turns back. Libra begins at the fall equinox, when day and night are the same length. He calls Cancer a solstice sign and Libra an equinox sign. Modern books fold these four signs into one group called cardinal. Cardinal means a sign that starts a season.
So both partners are born at a turn of the year. One is born as summer starts. The other is born as fall starts. Modern astrologers read the cardinal signs as starters, people who like to set things in motion. Two starters can build fast. They can also pull in two directions at once.
Ptolemy lists two more ways that two signs can be linked. Signs that command and obey sit the same distance from an equinox. Signs that behold each other sit the same distance from a solstice. I checked both lists in the Robbins notes, and in the degree by degree reading that William Lilly used in 1647. Cancer and Libra appear in neither, on either reading. The square is the only tie the old books give this pair.
Mars is weak in both signs
Each planet has signs where the old books call it strong and signs where they call it weak. These ranks are called dignities. Four of them matter here.
- A planet is at home in the sign it rules.
- It is in exile, also called detriment, in the sign across from its home.
- It is exalted in its sign of honor.
- It is in its fall in the sign across from that sign of honor.
Now apply them to Mars. In chapter 17, Ptolemy gives Mars two homes, Aries and Scorpio. Libra sits straight across from Aries, so Mars is in exile in Libra. In chapter 19, he puts the exaltation of Mars in Capricorn. Cancer sits straight across from Capricorn, so Mars is in its fall in Cancer. Lilly’s table of dignities, from Christian Astrology, keeps the same scheme.
So Mars is weak in both signs of this pair, for two different reasons. Only two other pairs share that trait, Cancer with Taurus and Libra with Taurus, since Mars is in exile in Taurus too. Cancer and Libra is the one pair of the three joined by a square.
Why this matters for a couple
In a reading, Mars stands for anger, courage and the push to act. It shows how a person fights and how a person goes after what they want. The old view is that a weak planet still works. It just works in a less direct way.
That lines up with the usual picture of this pair. Many modern pages say that Cancer and Libra both dodge a fight. The tradition gives a reason in its own terms. Mars, the planet that picks fights, is a guest in both signs, and not a welcome one.
How many real charts carry a weak Mars?
A dignity is a rule about signs. Your chart holds more than your Sun sign. So I asked a concrete question. Among people born with the Sun in Cancer, how many also have Mars in Cancer or in Libra? And the same for Libra Suns.
I tracked the Sun and Mars every six hours from 1600 to 2400. That is 800 years and over one million moments. For each moment, I noted both signs. The shares below are conditional. They count only people with the given Sun sign.
| Born with the Sun in | Mars in Cancer, its fall | Mars in Libra, its exile | Either one. |
|---|---|---|---|
| Cancer. | 15.14 percent of Cancers. | 9.30 percent of Cancers. | 24.44 percent of Cancers. |
| Libra. | 8.75 percent of Libras. | 15.27 percent of Libras. | 24.02 percent of Libras. |
| Any Sun sign, all of the time. | 9.40 percent of the time. | 9.58 percent of the time. | 18.98 percent of the time. |
About one Cancer in seven has Mars in Cancer. That matches our page on Mars in Cancer and our Cancer and Scorpio guide. About one Libra in seven has Mars in Libra. Each sign pulls its own weak Mars into many of its own charts.
Why the lopsided shape? When Mars sits on the far side of the Sun, it moves in step with the Sun for months. So Mars lands in the Sun’s own sign far more than chance, and in the signs next to it. That is why a weak Mars in your own sign is more common than the flat 1 in 12.
Now pair them up
Take a random Cancer and a random Libra. I treated their charts as unrelated, which is what the Voas census showed for signs. Here is the share of couples with the weak Mars.
| What the couple has | Share of Cancer and Libra couples. |
|---|---|
| Mars in Cancer or Libra, in at least one chart. | 42.6 percent, or about 2 couples in 5. |
| Mars in its own Sun sign, in at least one chart. | 28.1 percent, or a bit more than 1 couple in 4. |
| Mars in Cancer or Libra, in both charts. | 5.9 percent, or about 1 couple in 17. |
So the weak Mars is not a rare footnote for this pair. In about 2 couples out of 5, one partner or both carries it. The rest of the couples have Mars somewhere else. For them, the weak Mars is a fact about the signs, not about the people.
The rest of the dignity table
Mars is not the only planet with a stake in this pair. Here is the full picture for the seven planets the old books used.
| Planet | In Cancer | In Libra. |
|---|---|---|
| The Moon. | At home. | No special rank. |
| Venus. | No special rank. | At home. |
| Jupiter. | Exalted. | No special rank. |
| Saturn. | In exile. | Exalted. |
| The Sun. | No special rank. | In its fall. |
| Mars. | In its fall. | In exile. |
| Mercury. | No special rank. | No special rank. |
Two rows cross. Saturn, the planet of limits and time, is honored in Libra and exiled in Cancer. Mars is weak on both sides. The Sun is in its fall in Libra, so every Libra has the Sun in its fall. Our Libra sign page explains that rank.
Two gentle rulers
Each sign has a ruler, the planet at home there. The Moon rules Cancer. Venus rules Libra. In chapter 5, Ptolemy names three planets as kind by nature: Jupiter, Venus and the Moon. In chapter 6, he names two as female: the Moon and Venus. So the two rulers of this pair are both kind and both female in his scheme. They are the only two planets with both labels. Venus rules Taurus as well, so Cancer and Taurus share this trait. No other pair does.
That gives the square a soft center. The link between the signs is hard. The planets that own the signs are gentle. The planet that would drive a fight is weak on both sides.
How many real charts have the rulers at home? Our sign pages measured it over long windows. The Moon is in Cancer for about 8.2 percent of Cancers. Venus is in Libra for about 23.5 percent of Libras. So a Libra is about three times as likely as a Cancer to have its ruler at home.
Where each partner’s Venus can sit
Venus orbits closer to the Sun than Earth does. From here, it never strays more than about 47 degrees from the Sun. That limit boxes in each partner’s Venus.
| Venus sign | Share of Cancer Suns | Share of Libra Suns. |
|---|---|---|
| Taurus. | 8.70 percent. | None at all. |
| Gemini. | 29.44 percent. | None at all. |
| Cancer. | 24.10 percent. | None at all. |
| Leo. | 29.31 percent. | 8.89 percent. |
| Virgo. | 8.44 percent. | 29.25 percent. |
| Libra. | None at all. | 23.51 percent. |
| Scorpio. | None at all. | 28.97 percent. |
| Sagittarius. | None at all. | 9.38 percent. |
Two things follow. First, no Cancer has Venus in Libra, and no Libra has Venus in Cancer. Venus can never cross into the partner’s sign in this pair. Second, the two lists meet only in Leo and Virgo. I summed the chance that both land in the same sign. It comes to about 5.1 percent, or 1 couple in 20.
Compare the Moon. It moves through all twelve signs each month, so any Cancer can have any Moon sign. The chance that a Cancer and a Libra share a Moon sign comes out at 8.3 percent, or 1 couple in 12. So a shared Moon is more common in this pair than a shared Venus.
How the pair can play out day to day
Here the page turns from counts to tradition. What follows is how astrologers read the two signs. Treat it as a set of images to test against your own life, not as facts about any person.
What each partner brings
Cancer is a cardinal water sign. Water stands for feeling, memory and care. A Cancer partner shows love by looking after people. A meal kept warm. A text to ask if you got home. A room that feels safe to come back to.
Libra is a cardinal air sign. Air stands for ideas, talk and links between people. A Libra partner shows love through fairness and grace. A plan that works for both. A kind word at the right time. A home that looks good and feels calm.
Where they meet
Both signs start things. Both want peace in the home. Both are ruled by a gentle planet. In the old picture, the Moon asks for comfort and Venus asks for harmony. Those two wishes sit well side by side.
Where they rub
The friction comes from the square and from the weak Mars. Each partner holds back anger in a different way.
| Where it snags | What Cancer feels | What Libra feels | A small step that helps. |
|---|---|---|---|
| Anger. | Hurt that goes quiet and turns inward. | Tense when a mood has no clear cause. | Say the hurt in one short line, the same day. |
| Choices. | Unsafe while a choice stays open. | Rushed when asked to pick too fast. | Set a date for the choice, then keep it. |
| Social life. | Drained by too many plans. | Boxed in by too many nights at home. | Trade one night out for one night in. |
| Care. | Unseen when care comes as a fair plan. | Unthanked when effort is not read as love. | Name out loud what the other just did for you. |
None of these steps needs a chart. Any two people with different styles can use them. The signs only give a name to the pattern. The fix lives in plain talk.
Look past the Sun
A Sun sign is one point in a chart with ten planets and twelve houses. To read two people well, astrologers compare whole charts. That method is called synastry. It looks at how each planet in one chart meets each planet in the other.
For this pair, start with Mars. A Libra with Mars in Libra, or a Cancer with Mars in Cancer, carries the weak Mars inside their own chart. Our page on Mars in Libra covers that placement in full. Then look at the Moon and Venus, the two rulers.
Cancer’s other links work in other ways. Capricorn sits across from Cancer, and our guide to Cancer and Capricorn compatibility follows that opposition. Libra squares Capricorn too, and our page on Libra and Capricorn compatibility covers that square. Our guide to aspects in astrology covers the angles themselves.
If a birthday falls near a sign change, check it first. The guide to the 12 zodiac signs gives the real Sun dates for each sign. Our Cancer sign page shows how the start of Cancer moves from year to year.
How I measured this
You can redo each number on this page.
For the Sun sign shares, I used two daily birth files published by FiveThirtyEight. One comes from the Social Security Administration and covers 2000 to 2014. The other comes from the National Center for Health Statistics and covers 1994 to 2003. I found each moment the Sun changed sign with astronomy-engine, an open source sky library, in the tropical zodiac. I spread each day’s births evenly over its 24 hours in Chicago time. When the Sun changed sign that day, I split the births by the hours before and after.
For the pair rate, I assumed that partners’ birth dates are not linked, which is what Voas found. The chance of one Cancer and one Libra is then two times the Cancer share times the Libra share. For the ranking, I did the same for all 78 pairs.
For the census cells, I used Table 7 of the Voas paper. It leaves out couples with a birthday on the first of a month, since too many of those dates came from blanks the census office filled in. It also removes the excess of same sign couples. The expected count for each cell is the row total times the column total, divided by the grand total.
For Mars, Venus and the Moon, I took the position of each body every six hours from 1600 to 2400 with astronomy-engine. That is 1,168,776 moments. I kept the moments with the Sun in Cancer or Libra and counted the sign of each planet. As a second route, I ran a separate grid every seven hours, offset by two and a half hours. Both grids agree within 0.02 point on every share. The run gives Mars in Cancer for 15.14 percent of Cancers, the Moon in Cancer for 8.20 percent, and Venus in Libra for 23.51 percent of Libras. Those match the figures on our other pages.
For the couple shares, I combined the Cancer and the Libra results as two unrelated charts. For example, the chance that neither chart has Mars in Cancer or Libra is 75.56 percent times 75.98 percent. One minus that gives 42.6 percent.
For the days between birthdays, I timed the Sun from each degree of Cancer to the same degree of Libra, for every year from 1990 to 2030. Times are given in New York time.
For the old rules, I read Ptolemy’s Book 1, chapters 5, 6, 11, 13 to 17 and 19, in the Robbins version, with his notes. I checked the dignities against Lilly.
Frequently asked questions
Are Cancer and Libra compatible?
Astrology reads them as a square, three signs apart, with two gentle rulers, the Moon and Venus. Mars, the planet of anger, is weak in both signs. No study has shown that any sign pair lasts longer, so treat it as a lens, not a forecast.
How common is a Cancer and Libra couple?
In US birth data, about 1 random pair in 66 is one Cancer and one Libra. That puts it ninth of the 78 sign pairs, and second among the squares.
Why is Mars weak in Cancer and Libra?
Mars rules Aries, and Libra sits across from Aries, so Mars is in exile there. Mars is exalted in Capricorn, and Cancer sits across from Capricorn, so Mars is in its fall there. About 2 Cancer and Libra couples in 5 have Mars in one of these two signs in at least one chart.
Is every Cancer and Libra pair a real square?
By sign, yes. By degree, no. The gap between their Suns runs from about 60 to 120 degrees. With a 6 degree orb, about 36 percent of pairs have Suns in a true square.
Can a Cancer have Venus in Libra?
No. Venus never strays more than about 47 degrees from the Sun. A Cancer’s Venus falls between Taurus and Virgo. A Libra’s falls between Leo and Sagittarius. They can share a Venus sign only in Leo or Virgo.
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