Days from start to end date, inclusive.

I want to calculate the number of days a start date to an end date, inclusive. For example, Wed Jan 1st to Tues Jan 7th is 7 days when all dates are included.

I know that I can just compute the difference and add 1. But, I get this error message that is annoying me: "Duration units were removed."

Is there an elegant method to computing this?

I have considered accepting inputs for Wed Jan 1st to Wed Jan 8th, from the example above. It is technically still correct because the time component is 00:00 hrs. But, it makes it harder to communicate the date with others...