We have an internal AngularJS application that collections information about events and participants.

Some fields are required and some are optional. Unfortunately there are a few fields (like phone number) that are optional but required, the powers that be have requested that add something that make the user click an "Unknown" button. This is so the user has to say it's not known (or does't exist) instead of just accidentally leaving it blank.

Is there a better way of accomplishing this that I can present as an alternative. To me it seems like having to put that button or check the checkbox ruins the flow of the form (which can contain a dozen or more fields, with a few being of this optional/required format)

  • You should really add an image/mock-up of the form. It took a while to understand what you mean with "optional but required". Mar 23, 2018 at 5:28

3 Answers 3


This is a common request, especially from marketing teams. Push back, there was a reason it was created as optional in the first place.

People don't like entering data they don't have to. 12 fields is a lot and I can think of many services I can sign up to with fewer fields - even banks!

Inform the powers that be that your conversion rate will be higher with fewer fields. Point them to examples of other sign-up/register forms that are more seamless.

Finally, allow the user to amend or add that data after they have registered/signed up.

enter image description here

Data collected by FormStack

  • While I intuitively agree with fewer fields, better conversion, the statistics you show don't obviously seem to support that supposition... a four-field form only has a 4% conversion rate, and doubling the number of fields from 10 to 21 only reduces the rate from 28% to 21%. I suspect the problem is that each type of form is different, and therefore has different "levels of commitment" from the user towards their completion. I think it would be more interesting to see conversion rates of just "Contact" forms with between 4 and 10+ fields.
    – TripeHound
    Mar 27, 2018 at 9:48
  • Totally agree. I added the image with data in respect to event registration conversion rate. Comparing a survey form to a contact form isn't all that useful.
    – CalRowston
    Mar 28, 2018 at 7:42

Tough one here .. mandatory optional fields!

You could leave them optional, and if the users click on the Send/Save button it could prompt them with a dialog saying something like "You have left the following fields blank: phone number, etc.. This information is important if __ needs to contact you in the event of __. Are you sure you want to leave them blank?"


A few points:

The flow of the form doesn't have to be ruined as long as the form is setup correctly:

  • Tab Order correct
  • Space button on a checkbox selects the checkbox

I would additionally save the check state to the database so you can accurately tell which submissions explicitly have no number.

Preventing Misdirection

Additionally, there shouldn't be a weird "mandatory optional field" concept. If there is not a number available, you will just end up with weird data a lot:

  • 867-5309
  • 000-0000
  • 123-4567

A couple options though:

  • Just add some visual flare to show it is an important field.
  • Show the fields on the form when they aren't filled with a required checkbox

enter image description here

  • Show a modal when the form is submitted offering a second chance if the field was missed

enter image description here

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