What is the difference between calendar days and business days?

Calendar days count every day on the calendar including Saturdays and Sundays. Business days (or working days) only count Monday through Friday, making them ideal for project deadlines and shipping delivery estimates.

How do I add 90 days to today’s date?

Switch to the "Add / Subtract Days" tab, select today’s date, choose "Add", and enter "90". The tool will display the resulting target date along with the day of the week.

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Days Calculator

The Days Calculator lets you compute the exact calendar duration between any two dates or determine future/past dates by adding or subtracting days. It includes options to include or exclude the end date, count working business days (Monday to Friday) excluding weekends, and convert the result into weeks and remaining days.

Presets:

Select start date and end date to measure elapsed duration:

Start Date

End Date

Include end date in calculation (+1 day)Count only business / working days (exclude Saturday & Sunday)

Calculated DurationCalendar Days

30days

Equivalent to 4 weeks and 2 days

Business Days (M-F):

20 days

Weekend Days (Sat/Sun):

10 days

Accurate date arithmetic with UTC timezone normalization.

Elapsed Date Duration and Working Day Calculation

How this mathematical and clinical model is calculated

Duration (Days) = (End Timestamp - Start Timestamp) / (1000 × 60 × 60 × 24)

Calendar duration is computed by measuring the elapsed milliseconds between Universal Coordinated Time (UTC) dates to eliminate Daylight Saving Time (DST) artifacts. Business day calculations iterate through each day, omitting Saturday (day 6) and Sunday (day 0).

Step-by-Step Calculation Process:

Normalize both dates to 00:00:00 UTC.

Calculate total calendar days: (Date2 - Date1) / 86,400,000 ms.

If "Include End Date" is toggled, add +1 day to the total count.

Filter out weekend days (Saturday & Sunday) to compute total working business days.

Key Capabilities & Features

Calculate days between dates with optional inclusion of the end date

Business days vs weekend days calculation (excludes Sat/Sun)

Add or subtract days, weeks, months, or years from any baseline date

Breakdown into total days, weeks + days, and approximate months

Quick presets: Days until New Year, Summer, Halloween, Christmas, and 100-Day sprints

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Help & FAQ

Frequently Asked Questions: Days Calculator

Everything you need to know about tools in this section.

Yes. All calculations are executed using UTC timestamps and precise calendar arithmetic, preventing off-by-one errors caused by leap days or 23/25-hour Daylight Saving Time transition days.