What this calculator does
Date Calculator finds a new date by adding or subtracting a duration, or measures the duration between two selected dates. Units include calendar days, weeks, months, and business days. It is useful for schedules, project milestones, payment terms, travel planning, warranties, and other questions where counting dates manually is error-prone.
Calendar days and business days
Calendar-day calculations include every day of the week. Business-day calculations skip Saturdays and Sundays. They do not automatically exclude public holidays because holiday calendars differ by country, state, company, and year. If a deadline excludes holidays, review the result against the appropriate official calendar.
Why month results can differ
Months do not all have the same length. Adding one month to a date near the end of a month may land on the last valid date of the resulting month. For example, a calculation beginning on January 31 cannot produce February 31. For contract or billing work, confirm whether the governing rule means a calendar month, a fixed number of days, or the next business day.
Example and limitations
To estimate a ten-business-day review window, select the starting date, choose business days, and enter 10. The result skips weekends but not holidays. Date results are generated in the browser using the displayed local date and do not provide legal advice about filing cutoffs, time zones, or jurisdiction-specific deadline rules.
Common questions
Is the starting day counted? Addition normally moves forward from the selected starting date rather than treating it as day one; verify the displayed result against the rule you must follow. Are leap years handled? The browser calendar accounts for valid February dates. Why can two “one month” periods have different day counts? Calendar months vary from 28 to 31 days, so month arithmetic differs from adding a fixed number of days.
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