Date Calculator
Find the days between two dates, or add and subtract years, months, weeks, and days from any date.
Days Between Two Dates
Holiday Settings
From August 25, 2026 to September 25, 2026 is 31 days — 1 month.
Breakdown
- In weeks
- 4
- In days
- 31
- In hours
- 744
- Weekdays
- 23
- Weekend days
- 8
Show your working
Assumptions
- The end date is not counted, so the span is the number of nights between the two dates.
- Calendar months and years vary in length, so the years-and-months figure uses the real calendar rather than fixed 30-day months.
- Leap days are included wherever they fall in the range.
- Dates are treated as local calendar dates, with no time of day.
Add or Subtract from a Date
Business Day Settings
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Date facts
- Does the end date count?
- Only if you ask it to. By default the span is the number of nights between two dates; tick the option to count the end date as well.
- How many weekdays are in a month?
- It varies with where the weekends fall. A 31-day span starting on a Tuesday holds 23 weekdays and 8 weekend days.
- Why do years and months not convert to a fixed number of days?
- Because calendar months are 28 to 31 days long. The difference is counted against the real calendar, not an average month.
- Are leap days included?
- Yes, wherever one falls inside the range it is counted as an ordinary day.
How the Date Calculator Works
The Days Between Two Dates calculator finds the span from start to end, expressed as years, months, weeks, and days — in that order. Enable holiday tracking to see which US federal holidays fall within the range. Checking "Include end day" counts both the start and end date as part of the span. For time-based calculations in hours and minutes, try the time calculator.
The Add or Subtract calculator applies your chosen time increments (years, months, weeks, days) sequentially to a starting date. Enable business days mode so the Days field skips weekends and any selected holidays, giving you the accurate working-day result.
Common Use Cases
- Project Deadlines: Count how many days — or business days — remain until a deadline from today. For a simple countdown, try the day counter.
- Invoice Terms: Calculate Net-30 or Net-60 due dates by adding 30 or 60 business days to an invoice date.
- Contract Periods: Find the exact end date of a 6-month or 1-year contract starting on a specific date.
- Age & Anniversaries: Determine the number of years, months, and days between a birthdate and today — or use the age calculator for a full breakdown including hours, minutes, and seconds.
- Countdown Planning: Find how far away an event or holiday is in weeks and days.
Worked Example
Days Between: 1 January 2026 to 31 December 2026 = 364 calendar days, 261 business days (2026 is not a leap year). Add/Subtract: Starting 1 April 2026, add 30 business days = 13 May 2026 (weekends skipped). Subtract 6 months 15 days from 15 September 2026 = 28 February 2026.
Privacy & Data
Your data stays in your browser. All calculations run entirely client-side — no data is sent to a server. Your dates are never stored, logged, or shared.
Holiday dates are computed locally using standard rules for US federal holidays. Floating holidays (like MLK Day and Thanksgiving) are calculated accurately per year.
How date arithmetic works
Calculating the difference between two dates requires accounting for months of unequal length and leap years. The most reliable approach converts both dates to Julian Day Numbers — integers counting days from a fixed epoch — then subtracts. This avoids all month-boundary complexity and handles leap years automatically.
Business days vs calendar days
A calendar day count includes weekends and public holidays; a business day count excludes them. The difference matters for contracts, delivery estimates, and legal deadlines. A 5 business-day window starting Thursday can span up to 9 calendar days if a public holiday falls within it. This calculator counts calendar days only.
Date formats around the world
The US writes dates as MM/DD/YYYY (month first), the UK and Europe use DD/MM/YYYY (day first), and the ISO 8601 standard uses YYYY-MM-DD (year first), which sorts correctly alphabetically and is unambiguous across cultures. When sharing dates internationally, the ISO format eliminates the ambiguity of whether "04/05" means April 5 or May 4.
Adding and subtracting months
Adding months is not always straightforward — adding one month to 31 January could give 28, 29, or 31 February depending on the convention used. Most systems "clamp" to the last valid day: 31 January + 1 month = 28 February (29 in a leap year). This calculator follows the same clamping used by most financial and calendar software.
Related calculations
To exclude weekends and bank holidays, use the business days calculator. For the name of the day rather than a count, the day of the week calculator answers directly, and the week number tool gives the ISO week a date falls in.
Evidence & Methodology
How This Page Is Grounded
Method
Normalises the entered calendar dates and calculates elapsed whole days between them.
Important limitation: Calendar-day and elapsed-time answers can differ around local daylight-saving transitions; the page states which interpretation it uses.
Primary Sources
- ISO 8601 date and time format International Organization for Standardization
- ECMAScript Date Objects Ecma International / TC39
Quality Checks
Leap years, reversed dates and month/year boundaries are checked.
See how sources are selected and corrections are handled in our Editorial & Calculation Methodology, and which automated checks this page has to pass in How We Test.
Frequently Asked Questions
How does the date calculator work?
The Days Between Two Dates tab finds the exact span between two dates expressed as years, months, weeks, and days. The Add or Subtract tab applies time increments to a starting date to find a future or past date.
Can I calculate the number of business days between two dates?
Yes — enable business days mode in the Add or Subtract tab to skip weekends and US federal holidays when counting days. This gives accurate working-day results for project deadlines, invoice terms like Net-30, and contract end dates.
Is my date data stored when I use the date calculator?
All calculations run entirely in your browser — no data is sent to a server, stored, or shared. Holiday dates are also computed locally using standard rules for US federal holidays.