The Birthday-number effect is one of my favorites and is the most commonly shown attribute in humans. It is a subconscious tendency of people to prefer the numbers in the date of their birthday over any other numbers. The Birthday-number effect was reported for the first time in the year 1997 by Japanese psychologists Shinobu Kitayama and Mayumi Karasawa. It largely depends upon the age, gender, and sometimes on the personality of an individual. It is often observed that the effect is more prominent for numbers over 12.


In 1997, both the researchers Shinobu Kitayama and Mayumi Karasawa observed that the Japanese people very repeatedly do not tend to maintain and improve their self-esteem. This was unlike most of the Europeans and Americans. However, the research held with some western participants found that people do have some false beliefs. They feel that they are better than average and that they take credit for success themselves and blame other people for failures. They simply overestimate the chances of something good happening to them. These studies with the Japanese did not reveal such kinds of self-enhancing tendencies.

In some cross-cultural studies, it was seen that the Japanese reported self-esteem to be hurt more by the failures as compared to the one boosted by success. This was just the opposite of what was seen in the Europeans and the Americans.


Most of the people in this world like themselves only and thus they prefer the dates most associated with them as well. The birthday date signifies more of their own self. Despite the fact that the same date may even appear in many other contexts, they tend to have a liking of that number a bit more.

People who do not like themselves tend not to show the birthday-number effect. There is a similar kind of effect called the Name letter effect; which is related to the letters. The letter effect says that people tend to prefer the letters that are a part of their names and consider that specific alphabet lucky for them.

The birthday number effect and name letter effect are somewhat correlated. In psychological terms, the Number Preference Task can be used to know the internal self-esteem of a person. There is some evidence that shows that the effect has a huge impact on real-life decisions in many places.


A study shockingly revealed that there is an increase in a positive attitude of a person towards prices when they were manipulated to match their dates of birth. Thus, it results in a higher chance of purchase for that similar product than before. Contradictory to this, another study using the birth year as the price did not show the same results.

A study of having a liking towards the products found that participants who have high self-esteem liked the products more if the product names unknowingly involved their birthday date or letters of their name. Some field research that went into the impact of the birthday number effect on the bigger decisions of life is still controversial. Just like some people think a lot and then choose the house number or the number on their car number plate.


In the entire history, we can see that societies have had numbers that they consider to be special for them. Like in ancient Rome number 7 was considered auspicious. In Mayan Civilization, the number 13 was said to be sacred. Japanese consider three, five, or seven gifts for the sign of luck. In China, the number 8 is considered lucky and 4 is avoided whenever possible as it is considered unlucky there. Western countries consider the number 13 unlucky; thereby avoid numbering the 13th floor in most of the corporate buildings. This is hence given the term triskaidekaphobia, which means the fear of the number 13.


There were a lot of controlled experiments carried on numbers dating back to 1933. In the year 1933, a researcher named Dietz asked Dutch people to name the first number which comes to their mind between 0 and 99. Number 7 was mentioned as the most common number. The number 7 also came out to be most common in studies that asked people to name their favorite number.

In an online poll done by Alex Bellos, a columnist for The Guardian, more than 30,000 people from all over the world submitted numbers. Here also the same results were obtained with 7 being the most popular. All numbers under 100 were submitted at least once and nearly half of the numbers were under 1,000.

Marketing researchers named King and Janiszewski investigated number preferences in a very different way. They showed undergraduate students random numbers and asked them to answer quickly whether they liked the number, or not, or felt neutral. The number 100 had the highest percentage of people liking it ( approx. 70%). The lowest proportion of people was the one disliking the number 100. The numbers 1 to 20 were liked by 9% of people which was more than other higher numbers.

Name letter effect and birthday-number effect correlation on a plate:

  • The closely related field of letter preference research dates back to somewhat in the 1950s.
  • In 1985, Belgian psychologist Nuttin reported a very unexpected finding. He said that people tend to prefer, unknowingly, the letters of their own name. The name letter effect has also been replicated in many other follow-up studies in different languages, cultures, and alphabets.
  • It does not matter that participants selected their preferred letter from a random pair, or picked it from the top six of all letters in the alphabet, or whether they rated each individual letter.
  • Nuttin predicted that the driving force behind the name-letter effect is an unconscious preference for a person connected to the self. Hence, he concluded that there would also be a birthday-number effect.
  • In psychological studies, the birthday-number effect has been exploited to a large extent to measure a person’s self-esteem. The Number Preference Task is often used in combination with the Letter Preference Task. They are sometimes jointly called the Initials and Birthday Preference Task.

This Post Has 2 Comments

  1. Interesting effects.

    1. I’m glad you liked it 🙂

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Close Menu