The subtraction formula in cell A6 makes use of these numbers to find the number of days between the two dates 43405 - 42292 1113. SUM A125 Format column B1 as a date. It then adds 1 year from cell B2 resulting in 2020.
The formula in cell A6 uses Excels DATE function to ensure that the date 10152015 is entered and stored as a date value.
For example between 1 Jan 2020 and 15 March 2020 there are 2 months and 15 days. Between a future date and today. This also looks for 3 arguments. It is categorized in Excel as a DateTime Function.