Subtract the earlier date from the later date
Count the total number of calendar days between the two dates
Include leap years if the period crosses February 29
Exclude the start date if you need elapsed days only
Include both start and end dates if your rule requires inclusive counting
Use a date difference formula in spreadsheets or programming tools
Verify the date format before calculating
Adjust for time zones if the dates include times
Use built-in date functions when available
Manually count days month by month if needed