Date arithmetic & duration tool

Date Calculator (2026 & 2027)

Calculate exact calendar days between two dates or project forward/backward by adding or subtracting days. Inspect business-day summaries, exclude federal holidays, and export date lists to CSV—100% free with no signup required.

Choose calculation

Use between-dates or add-days mode.

Configure date range

Pick start/end dates and inclusion rules.

Quick Range Presets

Start date

End date

Include start dateInclude end dateExclude US federal holidays from business days

Total Days

4 days

Calendar span

Business Days

4 days

Working days

Weekends

0 days

Sat & Sun

Holidays

0 days

US Federal

Preview

Check the result before copying or exporting.

4 days

Weekday days: 4
Weekend days: 0
US federal holidays: 0
Business days: 4

First 20 included dates

Preview the full list via CSV export.

Date	Type
2026-05-04	Weekday
2026-05-05	Weekday
2026-05-06	Weekday
2026-05-07	Weekday

Export

Download CSV or share your settings.

Understanding Date Arithmetic: Calendar Days vs. Business Days

Accurate date calculation is central to business contracts, legal compliance, supply chain logistics, and personal planning. While adding simple numbers seems straightforward, date arithmetic involves several calendar anomalies including variable month lengths (28 to 31 days), leap years, weekend distributions, and federal statutory holidays.

Calendar Days (Elapsed Days)

Calendar days measure total solar days elapsed from point A to point B, without skipping weekends or holidays. Most commercial warranties, lease agreements, travel visas, and residential rental contracts define terms in pure calendar days.

7 days = Exactly 1 calendar week
30 days = Standard billing interval
365 days = Standard non-leap year (e.g. 2026, 2027)

Business Days (Working Days)

Business days strictly count standard operating days (typically Monday through Friday), excluding Saturdays, Sundays, and official statutory holidays. Banking clearing cycles (ACH, Fedwire), court litigation filings, and supply chain lead times operate on business days.

5 business days ≈ 7 calendar days
20 business days ≈ 28–30 calendar days
250–252 business days = 1 working year in the US

Common Commercial & Legal Day Intervals

Use this quick-reference matrix when calculating statutory deadlines, payment terms, or contractual review periods:

Day Interval	Calendar Weeks	Approx. Business Days	Primary Use Cases
10 Days	1.4 Weeks	6–8 Working Days	Legal response deadlines, court summons, formal defect cure notices
14 Days	Exactly 2 Weeks	10 Working Days	Standard two-week employment resignation, biweekly payroll cycles
30 Days	4.3 Weeks	20–22 Working Days	Commercial Net 30 invoicing, month-to-month lease termination notice
45 Days	6.4 Weeks	30–33 Working Days	IRS 1031 exchange identification window, mortgage loan contingencies
60 Days	8.6 Weeks	42–44 Working Days	Net 60 B2B vendor terms, US WARN Act advance plant closing notices
90 Days	12.9 Weeks	63–65 Working Days	Corporate quarterly financial audits, employee probationary review, Net 90 terms
180 Days	25.7 Weeks	125–130 Working Days	International passport 6-month validity rule, IPO insider lock-up expiration

The "Fencepost Problem" in Date Counting

One of the most frequent causes of dispute in contract law and deadline calculation is the difference between inclusive and exclusive day counting. Computer algorithms and mathematical subtraction evaluate elapsed time:

Elapsed Days = End Date - Start Date

If an employee takes leave starting Monday, March 2 and returning Thursday, March 5:

Exclusive Count: March 5 minus March 2 = 3 days of duration. This measures the 24-hour intervals between the two timestamps.
Inclusive Count: If both the start date and the end date are counted as leave days (Monday, Tuesday, Wednesday, Thursday), the total is 4 days.

WCalendar provides explicit toggles for both Include start date and Include end date, enabling you to match whichever convention your legal jurisdiction, insurance policy, or company guidelines require.

Does the date calculator count calendar days or business days?

The primary calculation displays total calendar days (all consecutive elapsed days including Saturdays and Sundays). Concurrently, the tool outputs an exact breakdown of business days (Monday through Friday) and weekend days, with an option to exclude official US federal holidays.

How does inclusive vs. exclusive date counting work?

Under exclusive counting (standard in elapsed duration arithmetic), day count equals End Date minus Start Date. For example, Monday to Wednesday is 2 days. Under inclusive counting (common in legal notices and court orders), both the start day and the end day are counted as active days, producing 3 days for the same span.

What happens if a calculated deadline falls on a weekend or federal holiday?

In commercial contracts and civil procedure rules (such as US Federal Rule of Civil Procedure 6(a)), if a deadline falls on a Saturday, Sunday, or legal public holiday, the period automatically extends to the next business day. Our tool lets you verify both the exact calendar target and the next available working day.

How do commercial Net 30, Net 60, and Net 90 payment terms work?

Standard commercial invoices specify Net payment terms in calendar days, not business days. A 'Net 30' invoice dated October 1 is due October 31 (30 calendar days). If you require 30 business days, that typically spans approximately 42 to 45 calendar days depending on intervening federal holidays.

How does the tool handle daylight saving time (DST) shifts?

All date arithmetic is calculated using calendar day intervals based on UTC calendar dates rather than raw millisecond math. This ensures that 23-hour 'spring forward' days and 25-hour 'fall back' days count strictly as 1 full calendar day without rounding errors.

Can I export calculated dates into spreadsheet software?

Yes. Click the 'Download CSV' button to save a structured CSV file containing dates, day of the week, weekend flags, and business day designations. You can open the file immediately in Microsoft Excel, Google Sheets, or Apple Numbers.