If you would like to calculate the number of years or months between two date fields, or a duration between today's date and a date field (such as a person's age based on Date of Birth), you can do so using our scripting language, Lua.

First, make sure that the Date fields you want to calculate on have slugs:

You'll also want to make sure that you have a Numeric field in your form to capture the difference between dates. This Numeric field should also have a slug:

For example, if you wanted to calculate the Age based on a Date of Birth, you would have one Date field slugged date_of_birth  and a Numeric field slugged age .

If you wanted to calculate the number of months between two home visits, you would have two Date fields, slugged home_visit_one  and home_visit_two , and a Numeric field slugged months_between_visits .

Once you have your fields properly slugged and set-up in your form, you can then write your script in the Scripting box.

If you'd like to compare an entered date with today's date (often to evaluate the age of a person), you can use the syntax below:

answers.age = difftimes(today(), answers.date_of_birth).year 

Where:

If you have two date fields in your form and you want to get the difference between the two, you can use the syntax:

answers.months_between_visits = difftimes(answers.home_visit_two, answers.home_visit_one).month 

Where:

Once you have added your script, click Save Changes.

When you create a new form result and enter in a date or two, the form will automatically calculate the difference.