# Date Calculator

> Free date calculator: count the days, weeks and business days between two dates, or add and subtract days from any date, with the day of the week.

Find the exact number of days, weeks, full months and business days between any two dates, or add and subtract days from a starting date to land on a future or past date.

*Interactive tool: enter your values at https://toollantern.win/date-calculator/ and results update instantly in your browser.*

## What this tool does

The date calculator has two jobs. First, it counts the time between any two dates: the exact number of days, how many full weeks that is, how many of those days are business days (Monday to Friday), and how many full calendar months fit in the range. Second, it does date arithmetic: give it a starting date and a number of days to add or subtract, and it tells you the resulting date and which day of the week it falls on.

## How the day count works

The count is the number of midnights between the two dates, which is the convention most date calculators use. From Monday to the next Monday is 7 days, and from January 1 to January 2 is 1 day. Each date is converted to a UTC timestamp and the difference is divided by 86,400,000 (the number of milliseconds in 24 hours), which keeps daylight saving transitions from ever shifting the answer.

## Worked example

From **2026-03-01** to **2026-03-15** there are **14 days**: exactly 2 full weeks. Counting only Monday to Friday gives **10 business days**. Adding **100 days** to 2026-01-01 lands on **2026-04-11**, a Saturday.

## Day of the week

The weekday is computed from the same UTC timestamp, so it agrees with any calendar. This is handy for checking, say, whether a deadline falls on a weekend before you promise a date to someone.

## Limitations

Business days are Monday to Friday only; public holidays are not subtracted, since they differ by country and region. Full months are whole calendar months: from March 15 to April 14 is zero full months, and to April 15 is one.

## Frequently asked questions
### How many days are between two dates?

Enter both dates above and the calculator shows the exact day count, plus weeks, full months and business days. The count measures midnights between the dates, so consecutive days differ by 1.

### How do I add 90 days to a date?

Use the add/subtract section: enter the start date, type 90, choose Add days. The tool shows the resulting date and its day of the week. This is useful for payment terms, notice periods and project timelines.

### What counts as a business day?

Monday through Friday. Weekends are excluded, but public holidays are not, because they vary by country and region. Subtract your local holidays manually from the business day figure.

### Is the end date included in the count?

The count is exclusive: it is the number of days you would add to the start date to reach the end date. From March 1 to March 2 is 1 day, not 2.

### Why use UTC for the calculation?

Days with daylight saving transitions are 23 or 25 hours long in local time. Converting dates to UTC timestamps first makes every day exactly 24 hours, so the day count can never be off by one around a clock change.

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Interactive version: https://toollantern.win/date-calculator/