The formula generator helps you build a countdown/countup field. It will tell you the number of days left or elapsed between now and the target date.
Note that "now" means the current local date of your computer. If your local time zone is different from the reference used by the SharePoint site, the calculation result might be off by several hours.
1/ Fill out the form. Based on your choices, the formula is automatically updated at the bottom of the form.
2/ Paste the formula in a calculated column in your list.
3/ Get the script available under the Downloads tab and link it to your page, under your list.
The steps are similar to the ones used for the color coded calendar. I plan to publish a tutorial in the future.