This document discusses date arithmetic in spreadsheets. It notes that manual date calculations can be tricky but spreadsheets make date calculations simple by allowing you to add or subtract numbers from dates. As examples, it shows how to calculate a date 79 days in the future by adding 79 to an initial date of 03/04/05. It also shows how to calculate the number of days between two dates, 05/10/05 and 12/08/70, by subtracting the dates. The document concludes by thanking the reader.