For every pair of individuals, the probability that both have the same birthday is equal to 365 / 2 = 23. This calculation is also useful in determining how many people are needed to have a greater than 50% chance of having at least one shared birthday with another person in a group.
Year of Birth
When a person’s birthday is known, the year of birth can be estimated by subtracting that person’s current age from their age at the time of the birthday. This method is particularly useful when a person’s complete age at the time of the birthday is not available and the individual needs to estimate the date of birth.
The formula to use for this is simply to calculate the number of years since an arbitrary date and then subtract that from the person’s age at the time of their birthday. This is easy enough to do in spreadsheet programs by entering a date into cell A1, the current month into cell A2, and the person’s birthday into cell A3. The result will be the number of full years (i.e., months and days excluding years) between the two dates.
This method is also useful when a person’s actual age at the time of their death is only available if the year of their birth is known. For example, a murder investigation may be able to identify the victim by using radiocarbon dating of tooth enamel. The results of the analysis will give a highly accurate estimate of the person’s year of birth and will thus enable police investigators to narrow down their search for possible matches.
Another method for estimating a person’s year of birth is to compare that person’s age at the time of a significant event with other people who are similar in age. This can be done in a variety of ways, such as by asking the person’s family members to compare notes, or by searching for other records of that same age group.
The “Year of Birth Unknown” category (along with its counterpart, Category:Date of Death Unknown) is intended for placement in the biographical entries for deceased individuals who were born in times and under circumstances that precluded the recording or preservation of historical data. This category is not to be used for persons who are alive, as they should be placed in Category:Living people or in the more specific Category:Possibly living people. A similar category, Category:Year of Death unknown, is for the placement of biographical entries for deceased persons who are believed to have died but whose year of death is not known. This should not be confused with the more general Category:Unknown date of death, which is meant to cover all cases where an individual’s date of death is uncertain.
Month of Birth
If you’re not interested in using a formula, but only want to determine how many days are left until your next birthday (or someone else’s), try this simple technique:
Using just the year and month of birth can provide you with a good estimate of someone’s age. In addition, this method is a good choice if you are working with data that may be considered personally identifiable and it’s not appropriate to share the full date of birth.
For example, if Bob’s birthday is May 12, 2024, you can find out how long he has been alive by subtracting 30 years from his birth date, which is 2024 – 30 = 1994.
This method is also useful for calculating the number of people in a group who have the same birthday. In this case, we use a simple probability calculation based on the fact that there are always 24 people in a group and the chances of finding one with your birthday are 1 / 2 * (1 + 23). Note that this method does not take into account leap years (such as the current year, which is a leap year). Therefore, the probabilities calculated do not necessarily reflect the reality of what would actually happen in real life.
Day of Birth
The day of birth, sometimes called the “birthdate”, is one of the most important pieces of information you have about yourself. The number of days between your birthday and the present is a key factor in your life’s journey, as it indicates how much longer you must go until you reach your next birthday. In addition, the day of your birth can be a powerful indicator of your character and personality.
While the month and year of birth are fairly straightforward to calculate, the day of birth can be more difficult. However, there are some methods you can use to estimate the date of your birth, even if you only know your age.
The basic technique involves using the decade number of your date of birth, converting it to a decimal, and then looking up that number in a calendar year table. If the year is odd, you can also add a one-year increment to the number to get the correct date of birth.
This method works best for dates with a few decades and a small number of years in between, because it allows you to reduce the numbers to single digits. It also makes the process faster and more accurate.
Another simple method involves subtracting a given number of calendar years from the current age to determine the person’s date of birth. This can be useful if you’re trying to find out when your friend or loved one was born. This is also commonly referred to as the running age method. It is less accurate than citing the complete date of birth, but is often used when only a partial date is known.
