How to use: Calculate date differences or add/subtract time periods from dates. Select Operation: "Calculate Difference" to find days between two dates, or "Add Time to Date" to find a future/past date. For difference: enter Start Date and End Date - results show total days between dates. For addition: enter Base Date, then Add Days/Months/Years (use negative numbers to subtract) - results show the new calculated date. Common uses: project deadlines (add 30 days to today), age calculations, contract expiration dates, rental periods, warranty tracking, payment due dates, and event planning. Examples: 90-day notice = add 90 days, 6-month contract = add 6 months, 2-year warranty = add 2 years.