How can I allow users to save and continue later

It is possible start a form and save it for later?.. I am building this for monthly report from the same 15 users each month. The idea is they could start filling the form, and append it some days during the month and then submit it at the end of the month

Is the saving part meant for you (as the form owner) or the user (your respondents)?

If it's for you, then our FORM BUILDER will automatically save your changes so you can start building your forms > leave it > then continue anytime you see fit.

If it's for your users so they can fill out the form > leave it > then continue where they left off, then you have 2 options to choose from:

1. Browser-based method

Easy to setup, but relies on the Browser's Local Storage. It's also commonly known as Autofill.

Meaning, if a user started filling out your form using Chrome, left their desktop/laptop, went back and re-opened the form on a different browser, then their progress is lost. Using that same Chrome browser again would allow them to continue where they left off.

Complete guide: How-to-Enable-Auto-Fill-on-Forms

2. Session parameter method

A bit complicated setup since it requires 2 forms to work.

FORM 1: The first form where the user will need to fill out the name and email field. The session URL will be created here and the email field will be used as the session ID.

FORM 2 (Main Form): This is the main form where all the necessary and important fields will be collected. The main form needs to have PAGE BREAKS. The progress on each page will only be saved when the "Next" and "Back" buttons are clicked.

Complete guide: How-to-Save-Forms-and-Continue-Later 

Have a look at the guides above and decide which better suits your needs.