Calculate time between dates

Updated at September 21st, 2020

This tutorial shows how to programmatically calculate the time between date values in your survey.  


In the example below, we want to calculate the time interval between dates entered for q3 and q4

Data processing code

For the time fields enter:

  • key: Create a key that can be easily found and identified (e.g. q3_q4)
  • start: Start date/time (e.g. q3)
  • end: End date/time (e.g. q4)
  • unit: Unit of measurement for the interval (e.g. month, year)


Example code

var rows = data.main;

// Enter key (new variable name for the time intervals) and start/end variables
var date_intervals = [
    {key: "q3_q4", start: "q3", end: "q4", unit: 'month'}, // q3 date to q4 date
    {key: "q4_q5", start: "q4", end: "q5", unit: 'month'}, // q4 date to q5 date


function getAbsoluteMonths(dt) {
  var momentDate = moment(new Date(dt))
  var months = Number(momentDate.format("MM"));
  var years = Number(momentDate.format("YYYY"));
  return months + (years * 12);

function getMonthsBetween(end, start) {
    if (end && start) return  getAbsoluteMonths(end) - getAbsoluteMonths(start)
    else return null

// Convert date strings to time intervals
rows.forEach(function(row) {
    _.each(date_intervals, function(entry) {
        if (row[entry.start] && row[entry.end]) {
            var start = moment(row[entry.start], 'YYYY-MM')
            var end = moment(row[entry.end],'YYYY-MM')
            row[entry.key] =  getMonthsBetween(end, start)

return rows

Resulting date/time intervals

Open your project (or refresh the page). The interval elements should be in fields because they were written into existence in the code. You can use the tree to search for elements if you're having trouble locating them. 

Reminder: For data processes, "Save" and "Run" the process after you are done editing the code view. To use the result of the process as the primary data for the project, you will need to set it as "Primary".
Data processes are specific to each project, and your code may not look identical to our example.

Your Protobi project may need different or more complex time calculations not yet written in our tutorials. Contact and we'll help you get setup for your case.

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