This template calculates a person’s current age based on a known age as of a specified date. This is useful when a reference states a person’s age at the time of the reference’s publication online age calculator

{{Age as of date|age|year|month|day}}

The age, year, and day must be supplied as natural numbers; a month can be specified as a natural number as well as by name or abbreviation (e.g., “August” or “Aug”).

The Gregorian calendar is assumed, with no special support provided for dual dating or the difference between Old Style and New Style dates.

If a reference dated July 4, 2019, mentions that someone is 50 years old, that person’s current age can be rendered using:https://www.agecalculator.help/

The person’s age is estimated as follows:

{{Birth year and age}}

Let us assume:

1. that the person in question was born sometime in 1966; and
2. that the present date is 31 January 2021.

• If the person was born after 31 January 1966 then they will be Error: Need valid year, month, day years old on 31 January 2021 as they have not had their 55th birthday yet.
• On the other hand, if they were born exactly on or before 31 January 1966, then they will be 55 years old.

Therefore, the template

displays their birth year and age as: 1966 (age 54–55)

• Optionally, if we know the person’s birth month but not the day, we can also have the template display the month.

Let us assume that the person was born in June 1966. Therefore:

• If it is presently January 2021, then this year the person has not had their birthday yet. Therefore, the template displays their birth year and age as 1966
• If it is presently June 2021, we do not know whether the person has had their birthday this year yet since their day of birth is unknown.
• Therefore, the template displays their birth year and age as 1966 (age 54–55).
• If it is presently December 2021, then this year the person has already had their birthday. Therefore, the template displays their birth year and age as: 1966 (age 55).

{{Death year and age}}

Let us assume:

1. that the person in question was born sometime in 1970; and
2. that they died sometime in 2020.

• We can posit as two extremes: (1) that the person was born on 31 December 1970 and died on 1 January 2020, in which case they would have been 49 years old at the time of their death as they did not achieve their 50th birthday on 31 December 2020; and (2) that they were born on 1 January 1970 and died on 31 December 2020, in which case they would have been 50 years old at the time of their death as they had their 50th birthday on 1 January 2020.

Therefore, the template {{Death year and age|2020|1970}}

renders their death year and age as: 2020 (aged 49–50)

• Optionally, if we know the month of the person’s death but not the day, we can also have the template display the month.

Using the above examples and assuming the month is 01 (January)

Therefore, the template {{Death year and age|2020|1970|01}}

displays their death year and age as January 2020 (aged 49–50)

If you wish to set out the full dates of birth and/or death of a person and thus to calculate their age accurately, please use the templates {{Birth date and age}} and {{Death date and age}}.

The term relative age effect (RAE), also known as birthdate effect or birth date effect, is used to describe a bias, evident in the upper echelons of youth sport and academia,

where participation is higher amongst those born early in the relevant selection period (and correspondingly lower amongst those born late in the selection period) than would be expected from the normalized distribution of live births. The selection period is usually the calendar year, the academic year, or the sporting season.

The difference in maturity – which can be extreme at young ages: a six-year-old born in January is almost 17% older than a six-year-old born in December in the same year- causes a performance gap that persists over time.

The term month of birth bias is also used to describe the effect and season of birth bias is used to describe similar effects driven by different hypothesized mechanisms.

The bias results from the common use of age-related systems, for organizing youth sports competition and academic cohorts, based on specific cut-off dates to establish eligibility for inclusion.

Typically a child born after the cut-off date is included in a cohort and a child born before the cut-off date is excluded from it.