Insert Value on "Add New Row" in subform

Insert Value on "Add New Row" in subform

I have a need to input a date value in a row as soon as as its added in a sub form, see below

Link to Form (with subform in it)

When I click add new in the sub form, I want the date field to be populated with the next day in sequence, based on the previous record. Which in turn will make the "Day" field value +1 of the previous row.

See the attached screen shot of what I'm trying to accomplish. 

Any help would be greatly appreciated