Date Calculator - Days Between Dates
Calculate the exact number of days, weeks, months, and working days between any two dates - Or add and subtract days, weeks, or months from a specific date. Instant results, no sign-up required.
Plan dates without spreadsheet math
Compare two dates, count business days, or jump forward and backward by days, weeks, months, or years.
Common Date Calculations
Whether you're planning a project, calculating a contract term, or simply curious, the table below shows the most frequently requested date calculations and their typical answers. To count down to a specific event, use the countdown to date tool instead.
| Calculation | Example | Answer |
|---|---|---|
| Days until New Year | Dec 1 → Jan 1 | 31 days |
| Days in a standard year | Jan 1 → Dec 31 | 365 days (or 366 in a leap year) |
| Weeks in a calendar quarter | 3 months | ~13 weeks |
| Business days in a month | Average month | ~22 working days |
| Fortnight in days | 2 weeks exactly | 14 days |
| 100 days from any date | Jan 1 + 100 days | April 11 (April 10 in leap year) |
Days in Each Month
A quick reference for how many days are in each month, including leap year differences. February is the only month that changes - It has 28 days in common years and 29 in leap years. If you need to see time zones alongside your date planning, check the world clocks tool.
| Month | Days | Days (Leap Year) | Notes |
|---|---|---|---|
| January | 31 | 31 | Unchanged |
| February | 28 | 29 | Leap year adds 1 day |
| March | 31 | 31 | Unchanged |
| April | 30 | 30 | Unchanged |
| May | 31 | 31 | Unchanged |
| June | 30 | 30 | Unchanged |
| July | 31 | 31 | Unchanged |
| August | 31 | 31 | Unchanged |
| September | 30 | 30 | Unchanged |
| October | 31 | 31 | Unchanged |
| November | 30 | 30 | Unchanged |
| December | 31 | 31 | Unchanged |
Memory tip: knuckle counting - Knuckles are 31-day months, valleys between them are 28–30-day months.
How to Calculate Working Days
A working day (also called a business day) is any day that is not a Saturday, Sunday, or public holiday. Most countries define their standard work week as Monday through Friday, giving 5 working days per week and approximately 260 working days per year. For time-based project work, pairing this with a Pomodoro timer can help structure your daily output.
The Basic Formula
To calculate working days between two dates manually: count the total calendar days, subtract the number of weekend days (Saturdays and Sundays), then subtract any public holidays that fall within the period. The calculator above automates the weekend calculation - Simply subtract holidays specific to your country or region.
A Note About Public Holidays
Public holidays vary significantly by country, state, and even company. The calculator above excludes weekends automatically but does not remove public holidays - Those are country-specific and must be accounted for manually. For example, a US-based 20-business-day deadline starting January 2 would typically land around January 30, but only if no federal holidays fall in that window.
Date Calculation Use Cases
Date calculations appear in nearly every area of professional and personal life. Here are the most common scenarios where knowing the exact number of days makes a real difference. For age-related calculations, you can also use our how old am I in seconds tool for a live, updating breakdown of your exact age.
| Use Case | What to Calculate | Example |
|---|---|---|
| Project deadlines | Business days from start | 20 working days from March 1 |
| Pregnancy milestones | Days/weeks from last period | 40 weeks = 280 days to due date |
| Age calculation | Days since birthday | How many days old am I? |
| Contract duration | Calendar days | 90-day contract end date |
| Lease end | Months from signing | 12 months from April 1 |
| Medication course | Days from start | 14-day antibiotic - When to stop? |
Leap Year Rules
A leap year adds an extra day (February 29) to keep the calendar synchronized with the Earth's orbit around the Sun, which takes approximately 365.2422 days. The Gregorian calendar uses a three-part rule. For holiday-specific date countdowns, the holiday timers page lets you see the exact days, hours, and seconds remaining until major events.
- A year is a leap year if it is divisible by 4 (e.g., 2024, 2028)
- Exception: Century years (divisible by 100) are not leap years (e.g., 1900)
- Exception to the exception: Century years divisible by 400 are leap years (e.g., 2000)
| Year | Leap Year? | Reason |
|---|---|---|
| 2024 | Yes | Divisible by 4 |
| 2025 | No | Not divisible by 4 |
| 1900 | No | Century year, not divisible by 400 |
| 2000 | Yes | Divisible by 400 |
| 2100 | No | Century year, not divisible by 400 |
Frequently Asked Questions
How are working days calculated?
Working days are calculated by iterating through every calendar day between the two dates and counting only those that fall on a Monday, Tuesday, Wednesday, Thursday, or Friday. Weekends (Saturday and Sunday) are excluded. Public holidays are not automatically excluded because they vary by country - Subtract them from the result manually.
Does the calculator account for time zones?
The calculator works with calendar dates only - It does not factor in time zones. When you select a date, it is treated as midnight in your local time zone. If you need precision across time zones, note the exact UTC time of both events and calculate the difference in hours first, then convert to days.
What date format should I enter?
The date inputs use your browser's native date picker, which automatically applies the correct format for your locale (MM/DD/YYYY in the US, DD/MM/YYYY in the UK and Australia, YYYY-MM-DD in many other countries). Simply use the calendar picker to avoid format confusion.
How do I add exactly one month to a date?
Use the "Add / Subtract Days" tab and select "Months" as the unit. Adding one month advances the date to the same day of the following month - For example, January 31 + 1 month = February 28 (or 29 in a leap year), because February doesn't have 31 days. This is standard calendar arithmetic.
Can I calculate negative dates or dates before 1900?
Most browser date pickers support dates back to at least January 1, 1000 CE, though display varies by browser. For historical date calculations before the Gregorian calendar reform of 1582, results may not align with the Julian calendar used at the time. For modern practical purposes (contracts, deadlines, birthdays), the calculator handles any date from roughly 1900 to 2100 accurately.