Online Age Calculator Between Two Dates or Age Calculator Online by Date of Birth. Here the tool is used calculate the age between the two dates entered. The age is calculated in years, months, and days. This tool is used to calculate age from one date to another or from date of birth to current date or till death.

Our age on Earth is based on Earth years. It is the number of times the Earth has orbited the Sun since the day we were born. If we were to live on another planet in the Solar System our age would be different because each planet takes a different amount of time to orbit the Sun. In other words each planet has a different year length.

There are actually two definitions of day:

1. Sidereal day is the time of rotation of the Earth relative to the stars.

2. Solar day is the time of rotation of the Earth relative to the Sun.

Our daily time keeping is based on the ‘mean day’, which is defined to be 24 hours. On Earth the solar and sidereal day are almost the same, with the former being three minutes 54 seconds longer than the later. (That’s why the stars rise almost four minutes earlier each night).

The general formula that many of us learn is rather simple and appealing. When you need to determine age in years and you want a fractional age (continuous values), a fairly well accepted industry standard approximates leap years with a quarter day each year

**AGE=int((NOW - DOB)/365.25);**

First determine the number of days from DOB to NOW, then divide by the number of days in a year. Because we have leap years, we use 365.25 as an average number of days in a year. Since AGE is always a whole number, we then use the INT (or FLOOR) function to grab just the integer portion of the result. This generally produces an accurate value for age, making it a nice solution for most applications.

Depending on how leap years fall relative to the date of death and birth, the approximation could be off by as much as what is essentially two days over the interval. Over a person’s lifetime, or even over a period of just a few years, two days will cause an error in at most the third decimal place.

Leap Year is the game chnager – if all years had 365 days, then we could just divide by 365, and the formula would always produce a correct value for age.

Society thinks of age as whole years, with ‘credit’ withheld until the date of the anniversary of the birth. The following equation (first proposed by William Kreuter) measures age in whole years. It counts the months between the two dates, subtracts one month if the day boundary has not been crossed for the last month, and then converts months to years.

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