Online Date Calculator is a practical time management tool designed to help you perform various date and time calculations. Whether you need to calculate project durations, countdowns to anniversaries, or project future dates, this tool delivers fast and accurate results.

This tool provides two core calculation modes：

• Date Difference Calculator: Enter a start date and an end date, and the tool will precisely calculate the difference in years, months, and days between them, along with total days, hours, etc., useful for project planning or time span analysis.
• Date Addition/Subtraction: Choose a starting date, then enter the number of years, months, days, hours, minutes, and seconds to add or subtract (use negative numbers to subtract). The tool will compute the exact resulting date and time.