Why are some numbers considered lucky or unlucky?

The short answer

Lucky and unlucky numbers are human inventions, so they vary by culture. They usually come from one of three places: the number sounds or looks like something else, it shows up in a religious or mythic story, or it matches something we see in nature.

The long answer

In a ​survey​ conducted by mathematician Alex Bellos, over 44,000 people cast their votes for their favorite number. Taking the crown with a whopping 9.7% of the vote was lucky number seven.

What makes seven considered a lucky number? And why does 13 get such a bad rap? Why are certain numbers considered lucky and others unlucky?

Disclaimer: Using the numbers presented in this article is definitely not a sure-fire method to win the lottery. Source: ​Reddit​

While I discovered there's a ​mathematical definition​ of a lucky number, I'll stick with the colloquial understanding.

Lucky and unlucky numbers are human creations, so they vary from culture to culture. There are wide-ranging reasons for why some numbers are considered lucky, auspicious, and sacred. But here are three main origins explaining how some lucky numbers get crowned and others cast aside as unlucky.

Note: I included several examples in each category, but this is definitely not an exhaustive list as there are too many to mention.

Origin #1: The number sounds or looks like something else.

Sometimes all a number has to do is sound or look like something else to be judged as lucky or unlucky.

Number	Lucky or Unlucky
4	Unlucky: In Chinese, Japanese, and Korean, the words for "4" sound similar to the words for "death."
8	Lucky: In Japanese kanji script, the number 8 is written as "八", which widens at the bottom. This shape suggests something growing, which is part of why it's considered a lucky number.
9	Unlucky: In Japanese, the word for "9" sounds like the word for "pain" or "suffering."
17	Unlucky: Some Italians are superstitious about 17 because the Roman numeral XVII can be rearranged to spell the Latin word "VIXI", meaning "I have lived" (which implies "I'm dead.")
39	Unlucky: In Afghanistan, 39 is considered highly undesirable, making cars with 39 on the license plate hard to sell. Some say the reason is that 39 translates to "morda-gow" (literally "dead cow"), a well-known slang word for a pimp. That said, I couldn't find any language spoken in Afghanistan where 39 sounds like "morda-gow." Another commonly told story is that a notorious pimp drove a car with a 39 on the license plate.

Origin #2: The number shows up in a religious or mythic story.

Many lucky or sacred (and unlucky or evil) numbers come from folklore or religious stories.

Number	Lucky or Unlucky
3	Lucky: Three shows up in many world religions and cultures, often representing completeness: In Ancient Egypt, gods and goddesses were often grouped in triads, usually representing a family unit (mother, father, child). In Hinduism's Trimurti, the three cosmic functions of creation, preservation, and destruction are personified as a triad of deities: Brahma the creator, Vishnu the preserver, and Shiva the destroyer. In Christianity, three is most prominently featured in the Holy Trinity (the Father, the Son, and the Holy Spirit). In Taoism, the Three Pure Ones are the highest gods, representing creation.
7	Lucky: Seven's lucky status is likely linked to how often the number shows up in many different religions: In Christianity and Judaism, seven is a sacred number because, according to Genesis, God created the world in six days and rested on the seventh. In Hinduism, there are seven higher worlds and seven underworlds. In Buddhism, the newborn Buddha takes seven steps.
13	Unlucky: In Norse mythology, there is a tale of Loki, the god of mischief, showing up uninvited to a banquet. Twelve gods were present, so Loki becomes the 13th god there. Loki ends up tricking another god into shooting his brother, making 13 an unlucky number.
13	Unlucky: In Christianity, 13 is also considered an unlucky number because of its ties to the Last Supper. Judas, one of the 12 disciples, was present at the supper and later betrayed Jesus. Since there were 12 disciples and Jesus present, that made 13 people at the table. Judas is referred to as the "13th guest."
666	Unlucky: In the Bible's Book of Revelation, John the Apostle refers to a beast, calling 666 the "number of the beast." This beast is often interpreted as the Antichrist, so 666 is considered a sign of the devil. While it's unclear exactly why 666 was noted, it may trace back to the practice of substituting Hebrew letters for numbers. A common interpretation of 666 corresponds to “Neron Caesar” in English, suggesting a link to Roman Emperor Nero who notoriously persecuted Christians.

Origin #3: The number matches something in nature.

We humans also notice certain numbers appearing in our observations of life on Earth.

Number	Lucky or Unlucky
3	Lucky: Three offers a feeling of wholeness because it often shows up in fundamental elements. You have birth, life, and death. A story has a beginning, middle, and end. Even a line has a starting point, middle section, and end point.
3	Lucky: A triangle is not only the strongest shape in engineering, but it also is the only polygon where every point is equidistant from each other.
3	Lucky: The Sumerians believed the universe was divided into three parts: the heavens, the earth, and the waters.
4	Lucky: In many Native American cultures, four is considered an auspicious number because of its presence in nature: four seasons, four directions, four times of day.
4	Lucky: Four-leaf clovers have been considered lucky for a long time by the Celtic peoples because of their rareness among the more normal three-leaf clovers.
7	Lucky: In ancient cosmology, there were accounts of seven visible heavenly bodies (Mercury, Venus, Mars, Jupiter, Saturn, the Moon, and the Sun) and the Moon's phases falling about every seven days. These observations coincide with ancient and medieval cosmologies, including Islamic and Jewish ones, which described seven heavens.
7	Lucky: Seven also shows up in many other natural phenomena, like seven colors in a rainbow, seven continents, and seven notes in a musical scale. It's also the only number between 2-10 that is neither a multiple nor factor of the other numbers.

🧠 Bonus brain points

Why is Friday the 13th unlucky?

Every 212.35 days, we experience the dreaded Friday the 13th. If that day has you feeling fearful, you may be afflicted with paraskevidekatriaphobia (fear of Friday the 13th). But why is this date so feared and unlucky?

While there isn't a single exact origin for why Friday the 13th is a common superstition, the number 13 and Friday have long been regarded as unlucky in many cultures. As covered above, 13's unlucky status has roots in Norse mythology and Christianity.

Biblical stories also likely contribute to Friday's perceived unluckiness. Many bad things are traditionally said to have happened on Fridays, including Jesus' crucifixion, the day Adam and Eve ate the forbidden fruit in Eden, the day Cain murdered his brother Abel, the day the Temple of Solomon was destroyed, and the day the Great Flood began.

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Sources

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