Date Calculator

Days between · Add / subtract · Business days

Start Date

End Date

Day count mode ?

Business day options

Weekend ?

Holidays (optional) ?

Quick examples

📌

Business days follow NETWORKDAYS style: both endpoints count when they are workdays. Holidays are optional extras.

📅 Enter dates to find the difference or a new date after adding or subtracting.

Date Calculation Formulas

A date calculator answers two jobs: how much time sits between two dates, and what date you land on after adding or removing time.

Days between dates

Calendar days = End − Start Exclusive count of midnights crossed Inclusive = End − Start + 1 Example: 1 Jan → 31 Jan exclusive = 30 · inclusive = 31

Add or subtract days

Result = Start ± N days Example: 15 Jun 2026 + 30 days = 15 Jul 2026

Business days

Workdays = weekdays in [Start, End] − holidays Matches NETWORKDAYS: both ends count if workdays WORKDAY walks N workdays after Start (start not counted)

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Use inclusive mode for “how many calendar dates are covered.” Use exclusive mode for “how many days until.”

Modes & FAQ

Mode	Inputs	Main output
Days Between	Start + End	Calendar & business days
Add / Subtract	Start + amount + unit	Result date
Business add	Start + N workdays	Date N workdays away

How do you calculate days between two dates?

Enter start and end dates. Exclusive mode shows end minus start. Inclusive mode adds one so both dates are counted.

How do I add days to a date?

Open Add / Subtract, choose Add, pick Days (or weeks, months, years), enter the amount, and read the result date.

How to Use This Date Calculator

Choose Days Between to measure a span, or Add / Subtract to project a new date. Business day options apply to both modes: weekend definition and optional holiday list as YYYY-MM-DD values separated by commas.

Results show the primary answer in the hero, calendar and business day chips, a Y / M / D breakdown for spans, weekday labels, a chart of weekday versus weekend mix, and step by step notes.

What is a date difference?

A date difference is the elapsed calendar time from one date to another. People ask for days until an event, length of a project, or how many nights between check in and check out. Exclusive days match “days until.” Inclusive days match “dates covered.”

How to calculate days between dates manually

1. Write both dates. 2. Convert each to a day serial or count midnights on a calendar. 3. Subtract. 4. For inclusive counting, add one. Leap years insert 29 February when the span covers that day.

Worked exclusive example: Start 1 March 2024, End 1 April 2024. March 2024 has 31 days, so exclusive days = 31. Inclusive days = 32.

How to add or subtract months and years

Adding one month to 31 January lands on the last day of February (28 or 29). Adding one year to 29 February 2024 lands on 28 February 2025 in this calculator. That clamp rule keeps every result a valid Gregorian date.

Business days and NETWORKDAYS

Microsoft Excel NETWORKDAYS counts whole working days between two dates and includes both endpoints when they are workdays. This calculator mirrors that for the business day span. Holidays you list are removed if they fall on an otherwise working day.

WORKDAY style projection (Add / Subtract with Business days unit) moves forward or backward by N workdays and does not count the start date itself. Example: Monday + 1 business day = Tuesday.

Weekends in the span

For a Days Between result, weekends in span counts Saturday and Sunday dates that fall inside the inclusive closed interval from the earlier date to the later date. That helps explain why business days are lower than calendar days.

Common mistakes

Mixing exclusive and inclusive counting when comparing tools
Assuming every month has 30 days when adding months
Forgetting holidays in a business day deadline
Using local time zone midnight differences when only dates matter
Reversing start and end without noticing the absolute span is the same

Practical scenarios

Project managers track calendar versus workday length. Recruiters set offer deadlines N business days out. Travelers count nights between hotel dates. Students count days until an exam. Finance teams schedule settlement dates that skip weekends.

Pair this tool with the Age Calculator when the span starts on a birth date, or the Due Date Calculator when dating a pregnancy rather than a general project interval.

Inclusive versus exclusive examples

Event from Friday 1 May to Sunday 3 May. Exclusive days = 2 (two midnights). Inclusive days = 3 (Fri, Sat, Sun). A hotel stay checking in 1 May and checking out 3 May is usually two nights, which matches exclusive days. A “three day festival covering those dates” matches inclusive days.

ISO week number

The start date ISO week follows the ISO 8601 week date system: weeks start on Monday, and week 1 is the week with the year’s first Thursday. The calculator reports the ISO week of the start date so you can label project weeks the same way many European schedules do.

Settlement and SLA style counting

Some contracts say “within five business days of notice.” That often means WORKDAY style counting from the notice date, not counting the notice day itself. Use Add / Subtract with Business days and amount 5. If the contract instead says “five business days between date A and date B,” use Days Between and read the business day chip (NETWORKDAYS style).

When this calculator is useful

Use it for days between any two dates, add or subtract days weeks months or years, project N business days ahead, and compare calendar days with Monday to Friday workdays.

Custom weekends

Not every workplace uses Saturday and Sunday off. Some regions treat only Sunday as the weekly rest day. Use the Weekend selector for Saturday + Sunday, Sunday only, or Saturday only. Business day counts and business day adds both respect that choice along with any holidays you list.

When this calculator may not be enough

It does not load a full government holiday calendar by country. You must enter holidays you care about. It does not handle non Gregorian calendars or shift schedules with rotating weekends beyond the weekend selector.

How to interpret your result

In Days Between mode the hero shows calendar days (per your inclusive setting). Chips repeat calendar and business totals. In Add / Subtract mode the hero shows the result date and its weekday. The chart appears for spans to show weekday versus weekend mix.

Leap years in day counts

If your span includes 29 February, that day adds one to the calendar day total just like any other date. Exclusive and inclusive modes both see it. Month add from 29 February into a non leap year clamps to 28 February.

Limitations

All math uses the Gregorian calendar in the browser. Month and year adds clamp oversized day numbers. Business day holidays are only those you type. Results are educational and planning aids, not legal filing deadlines unless your policy matches these rules.

⚠️

Confirm contractual deadlines with the calendar your contract names, including local holidays.

ℹ️

Business day counting aligns with Excel NETWORKDAYS and WORKDAY behavior described in Microsoft documentation.

How do you calculate business days between dates?

Count Monday through Friday dates from start through end, then remove any listed holidays that fall on those weekdays. Both endpoints count when they are workdays.

How do I subtract days from a date?

Use Add / Subtract, choose Subtract, enter the amount and unit, and read the earlier result date. Business day subtract walks backward skipping weekends.

What is the difference between calendar days and business days?

Calendar days include every day. Business days include weekdays only and may exclude holidays. A seven calendar day week usually has five business days.

Does adding one month always add 30 days?

No. Adding months moves the calendar month and keeps the day number when possible. Short months clamp the day. Adding 30 days always moves exactly 30 midnights.

Sources & References

Microsoft Support: NETWORKDAYS function: support.microsoft.com
Microsoft Support: WORKDAY function: support.microsoft.com/en-us/excel/functions/workday-function