If the dates of the two days are not too far apart, it may be easiest to just count them by hand, using a calendar for reference. Otherwise, some websites, such as TimeAndDate.com, offer resources online for calculating the number of days between two dates. These are known as date or date duration calculators.
TimeAndDate.com provides an online date duration calculator. To navigate to this calculator, go to TimeAndDate.com, hover your mouse over the Calculator tab located at the top right, and then click the Date to Date Calculator selection in the drop-down menu. To use the calculator, input a start date and an end date, and click the green Calculate Duration button. Alternatively, you can also enter a start and end date by selecting them from the provided drop-down calendar.
The TimeAndDate.com calculator also includes options to only count work days or to add time fields and time zone conversions. If you become confused or need help at all while using the calculator, the website provides a link to a page with information on how to use the calculator, along with some examples to refer to. The page also contains links to other date calculators that may come in handy.