What is a Day Calculator?

A Day Calculator is a web app that calculates the days between two dates, or adds or subtracts days to produce a future or past date. It is used to calculate due dates, plan events, timelines and milestones, and academic deadlines. Rather than calculating it yourself, you can use the Day Calculator to take advantage of the rules of the calendar, leap years, etc. and get results quickly and accurately.

How Does the Day Calculator Work?

• Select your mode: Days between Dates or Add (and/or) Subtract Days.
• Enter your dates: either select a Start Date and End Date, or select a Start Date plus the number of days added/subtracted.
• Optional: show results in weeks + days and/or show the results in business days (Mon–Fri), and optionally select inclusive counting.
• Click Calculate and receive your results instantly.

Example: From Jan 1 to Mar 15 (same year) = 73 days (exclusive), or 74 days (inclusive) by counting both dates.

Formulas Used

Days between dates (exclusive):

• Days = (End Date − Start Date) in calendar days.
• Inclusive count: add +1 to include both endpoints.

Add/Subtract:

• Target Date = Start Date ± N days (calendar arithmetic).

Leap years are handled automatically. When business days are selected, weekends (Sat–Sun) are excluded from the count.

Key Benefits of Using This Day Calculator Online

• Fast & accurate: nothing to count on your own, and no spreadsheet formulas to memorize.
• Two modes: days between and add-subtract days, all in one place.
• Flexible outputs: calendar days, weeks + days, and business days.
• Planning utility: useful for project timelines, planning leave, event dates, and due dates for assignments.
• Mobile utility: easy to run on your phone, tablet, and desktop.

Practical Example Use-Case

• Countdown to a deadline: Enter today as Start Date and your due date as End Date to get the remaining calendar days (and optional business days).
• Find a future date: Choose Add Days, enter +100, and instantly see the exact date 100 days from your start.
• Work scheduling: Use business days to plan 10 working days ahead for approvals or deliveries.