Calculate time between 2 dates

[evanshart]

Dear all,

Is there a way to 'calculate' the time between 2 dates?
I want to know how long ago the participant was diagnosed with an illness.
So one question will be "When were you diagnosed?"
Another question will be "What is today's data?" [though I know this can be caught as metadata too]
And then I want ODK to calculate the time between these two.

Many thanks in advance!
Johnny Evans

[danbjoseph]

Calculating difference in days is possible. Use a calculate type question with the following expression:
round(decimal-date-time(today()) - decimal-date-time(${date_diagnosed}))

Calculating the number of months or years is more complicated, see this post for details:

Calculate age

The following will calculate the age, in days, from their date-of-birth: calculate = "round(decimal-date-time(today()) - decimal-date-time(${dob}))" (I round because due to floating point truncation you can sometimes get a difference of, say, 1233.999998 days. If you blindly truncate this you could end up a day off). Although it seems innocuous to be asking for months and years, in reality the question is ill-posed. Specifically, what precisely is a "year"? Some years can be 365 days, others…

And here's a post that explores calculating age:

Using Date of birth to restrict further capturing

Leap years and such make it challenging to calculate age. Can you ask the respondent's age and then use that answer to control the rest of the survey? I've modified your survey to use the int((${doi} - ${respondent_dob}) div 365) to calculate the age. And you can see that it doesn't work sometimes if the month/day of the two dates are close. age_check.xlsx (14.2 KB) Correct: [Screen Shot 2022-02-09 at 10.26.22 AM] Wrong: [Screen Shot 2022-02-09 at 10.26.31 AM] Correct: [Screen Shot 2…