Depending on business vertical, there are different types of forms that lead to conversions. Some of these forms may include contact us forms, forms for gated content, or registration forms.

Be it any analytics solution you are using Adobe Analytics or Google Analytics etc

Form filling have many fields. If we start tracking all the fields and fire server call on each interaction it will be an additional cost.

To keep the tracking cost effective with relevant information following 4 step approach works good.

Step 1: Track the form impression.

When using Adobe Analytics to track forms, the first thing that should be tracked is the impression (also known as when the user first views the form). There can be many ways a user comes to a form. They can scroll up or down to view a form, they can click on a button that directs them to one, or they may navigate to a contact us page where they fill out their information.

Step 2: Track form interactions i.e form start

If highly required you can track some other interactions may include filling out a field, checking a box, or clicking a submit button. When tracking those interactions in a funnel analysis, it’s important to track which field they interacted with first.As said earlier that each interaction will be addition server call.

If you have a wizard form, which is basically a multistep form. A great example of a wizard form is when you are purchasing something online and your first step is to log in. Then, your next step would be to select the item and fill out your credit card information. After clicking a “next” button or a button that moves you forward in the process, you may move on to filling out a mailing and shipping address. Tracking each step of the wizard including starts, interactions, and completes is valuable to understanding the user’s journey.

Step 3: Track your submissions.

Submitting the form is the next step of tracking, which is basically when you hit the “send” button when it is not truly complete. A business user of Adobe Analytics may want to know how many time’s a user submitted the form and either completed successfully or failed during data entry.

Step 4: Track your form completions. Form completion is the last stage of tracking

While the cost is a factor when you track form filed interaction for each field,generally clients are interested to learn of where users drop/abandon a form.
For example, if your form has three sections, and each section has 6 fields, where does the user drop/abandon the form?
Tracking form and its analysis can offer insights to what optimization can you make to enhance the conversion rate.
Server call is associated to cost and you will need to evaluate the cost / benefit analysis for your organization.