Date Calculator — Days Between Dates & Date Math Free

How many days between two dates? What date is 90 days from now? These simple questions are surprisingly hard to answer mentally because months have different lengths, leap years add complexity, and crossing year boundaries makes counting unreliable. Our Date Calculator handles all of this instantly.

What Is a Date Calculator?

A date calculator performs two types of operations: calculating the difference between two dates (in days, weeks, months, and years) and adding or subtracting a number of days from a given date. Both operations account for varying month lengths, leap years, and calendar rules.

How to Use Our Date Calculator

1. To find the difference: enter a start date and end date. The calculator shows the gap in days, weeks, months, and years.
2. To add/subtract days: enter a starting date and the number of days to add (or subtract with a negative number).
3. The result includes the day of the week for the target date.
4. Optionally exclude weekends to calculate business days only.

Why Use an Online Date Calculator?

• Accuracy: Accounts for leap years, varying month lengths, and year boundaries that make manual counting error-prone.
• Business days: Exclude weekends for project planning, legal deadlines, and business timelines.
• Bidirectional: Both date difference and date arithmetic in one tool.
• Day of week: Know what day of the week any date falls on — useful for event planning.

Common Use Cases

Project managers calculate deadlines — "the deliverable is due in 45 business days" translates to a specific calendar date that the calculator finds instantly, accounting for weekends.

Legal professionals determine statute of limitations dates, filing deadlines, and contract milestones that are specified as a number of days or months from a triggering event.

Event planners count down days until a wedding, product launch, or conference to coordinate preparation timelines and vendor schedules.

Tips and Best Practices

• When counting "days between," clarify whether the start and end dates are included. "January 1 to January 3" could be 2 or 3 days depending on the convention.
• For legal and financial deadlines, check whether the jurisdiction counts business days or calendar days, and whether holidays are excluded.
• Use the business days option for project planning. A 30-calendar-day timeline is actually about 22 business days — a significant difference for scheduling.

Ready to try it? Use our free Date Calculator now — no signup required, works entirely in your browser.

Frequently Asked Questions

How do I calculate days between two dates?

Enter the start and end dates in our calculator. It accounts for varying month lengths, leap years, and provides the result in days, weeks, months, and years.

How many business days are in a month?

A typical month has 20-23 business days (weekdays), depending on the month length and which days of the week it starts and ends on. The average across a year is about 21.7 business days per month.

What date is 90 days from today?

Use our calculator to find the exact date. 90 calendar days is approximately 3 months but varies depending on which months are involved (28-31 days each).