# The age calculator on the website sometimes gives an age that is slightly different than if I calculate by hand using the instructions in the User's Guide. Why does this occur?

The age calculator on the [website](/content/free-resources/asq-calculator/index.html) and in the app stores uses an actual calendar to calculate a child's age. It takes into account which months have 30 days and which months have 31 days, and therefore provides a more precise age calculation. For ease of use, the manual calculation described in the User's Guides assumes that every month has 30 days. Ages calculated by hand may have a difference of a couple of days from ages calculated with the calculator.

#### Tags

[ASQ-3(195)](https://support.agesandstages.com/kb/tag/138) [ASQ:SE-2(123)](https://support.agesandstages.com/kb/tag/143) [User's Guide(37)](https://support.agesandstages.com/kb/tag/151) [calculator(8)](https://support.agesandstages.com/kb/tag/152) [ASQ Calculator app(4)](https://support.agesandstages.com/kb/tag/153)