Days between dates calculator

How days are counted

The calculator counts the number of calendar days between the start and end date, inclusive of the start date but not the end date. This is the standard convention, the same way you count the days in a hotel stay or a project duration.

Business days exclude Saturdays and Sundays. Public holidays are not excluded, as these vary by country and region. If you need to exclude specific holidays, subtract them manually from the business days count.

Common uses

• Calculate contract or project durations
• Find out how many days until a deadline, event, or holiday
• Count business days for payment terms such as net-30 or net-60
• Calculate notice periods for employment or leases
• Determine how many days have passed since an event

Inclusive vs exclusive counting

The "start inclusive, end exclusive" convention (also called half-open interval) is the most common in both everyday use and programming. Under this convention:

• A hotel stay checking in on March 1 and checking out on March 4 is 3 nights (March 1, 2, 3)
• A project running from Monday to Friday is 5 days
• A 30-day trial starting January 1 expires on January 31 (day 30 is January 30, the last full day)

Some legal contexts use fully inclusive counting (both start and end dates count), which adds one day. If a law specifies that an appeal must be filed within 30 days of a decision dated January 1, and both the decision date and the filing date count, the deadline is January 30, not January 31. When precision matters legally, always verify which convention applies.

Converting days to other units

The month and year conversions are approximate because months have different lengths and years vary by leap year. For exact month or year counts, use the age or date difference calculators that apply calendar-aware arithmetic rather than dividing by an average.

Business days in practice

A calendar month contains roughly 20 to 23 business days depending on how weekends fall. A year contains 260 to 262 business days (52 weeks × 5 days, ±1 or 2 depending on where January 1 falls). These figures exclude public holidays, which further reduce the count by 8 to 12 days in most countries.

For payment terms: net-30 in most commercial contexts means 30 calendar days, not 30 business days. Net-30 business days would be approximately 6 weeks. Always check whether a payment term specifies calendar or business days, as the difference is material for cash flow planning.

For employment notice periods: a 2-week notice period typically means 14 calendar days in most jurisdictions, not 10 business days — though this varies by country and employment contract. Legal notice periods in some countries are expressed in working days, which requires knowing the local public holiday schedule to calculate precisely.

Practical examples

Project deadlines

A project starting on April 7 with a 90-day duration ends on July 6. If the contract specifies 3 months instead, it ends on July 7 — one day later, because months are used rather than a raw day count.

Payment terms

An invoice dated March 15 with net-30 terms is due April 14. An invoice dated March 1 with net-30 is due March 31. The due date shifts with every invoice date, making a calculator more reliable than mental arithmetic for accounts payable management.

Lease and tenancy

A 12-month lease starting September 1 ends on August 31 the following year — not September 1. The tenant has the right to occupy through August 31, which is 365 days (or 366 in a leap year). A lease ending on September 1 would be a 13-month lease by convention.

Age of events and records

Knowing the number of days since a historical event, the founding of a company, or the start of a conflict gives a precise measure that avoids ambiguity about how to count partial years. The days-between calculator gives this directly as an integer.