Age calculation

[CUARTA_OPORTUNIDADLOCAL]

how to subtract two dates to calculate the age

I have this survey, there is the question of today's date, then I bring the date of birth, but by subtracting both dates in the next question it makes me wrong.

[ChelseaRozek]

Ismael has an example in his blog post: https://community.esri.com/groups/survey123/blog/2016/04/17/dates-and-time-in-survey123-for-arcgis 

	EPOCH Format	Decimal Date Format
Calculate age from birthday	int((today() - ${birth_date}) div (1000*24*60*60* 365.25))	int((decimal-date-time(today()) - decimal-date-time(${birth_date})) div 365.25)

Also, it looks like you're missing the proper ${fieldname} notation in your calculation.

You can use today() in the calculation to automatically get today's date without having to use another question in your survey

[TRDSYSTEMS]

Greetings,

This was quite helpful. Decimal Date format works with both connect and the web as opposed to the EPOCH Format which appears to work with the Field app only. Question: how can you do a calculation for the age of a baby in months? I was able to get the calculation to work in years but what formula can I use to calculate the age of a baby in months?

[ChelseaRozek]

If you multiple it by 12, you will get months:

((decimal-date-time(today())-decimal-date-time(${birthday})) div 365.25)*12

You can use this reference guide to tweak the result with either int() or round() depending on what value you want. 

Formulas—Survey123 for ArcGIS | Documentation 

You could get really fancy with if() and calculate years if the birthday is further away than 1 year or months if the birthday is less than 1 year in the one field, though you may want it to be a text field so you could append "months" or "years" on the end so it's not confusing.

if(condition, a, b)

If true, returns a; otherwise, returns b.