hide entry field based on date

I'm doing a registration form. I need to change the registration fee based on the current date (the fee goes up after the early registration deadline). How can I do this?

If you want to hide a fields based on a date, simply use the Show/ Hide Field option: http://www.jotform.com/help/316-How-to-show-or-hide-a-field-in-the-form-based-on-the-other-field-input-or-selection

You could create a condition like this: 

Here is a guide for you to update a fields value based on date selection: http://www.jotform.com/help/268-How-to-Insert-Text-or-Mathematical-Calculation-into-a-field-using-a-Condition

If you need further help, let us know what your form is, and what you have worked on so far, so we can inspect and advice you.