Date Calculator – Days Between Dates, Add & Subtract Dates
Find the exact number of days between two dates, add or subtract days, weeks, months, or years from any date, count business days, and track countdowns all free with no sign-up required.
Options
Select dates and click Calculate Date
This date calculator performs two types of calendar arithmetic. The Date Difference tab measures the exact span between any two dates in days, weeks, months, and years. The Add / Subtract tab finds the resulting date after adding or removing a period from a starting date.
- Calendar days: Count every day including weekends
- Business days: Skip weekends and US holidays
- Countdown mode: Days remaining to a future date
- Add days/weeks/months/years to any date
- Subtract to find a date in the past
- Day of week for any result date
| Month | Days |
|---|---|
| January | 31 |
| February | 28 / 29* |
| March | 31 |
| April | 30 |
| May | 31 |
| June | 30 |
| July | 31 |
| August | 31 |
| September | 30 |
| October | 31 |
| November | 30 |
| December | 31 |
* 29 days in leap years
How to Use the Date Calculator
The calculator has two tabs. Choose the one that matches your task, fill in the fields, and click Calculate Date. Use Show Full Breakdown to expand the result into every unit years, months, weeks, and days at once.
Finding the Number of Days Between Two Dates
Open the Date Difference tab. Pick a start date and an end date using the calendar pickers. Click Calculate and the result shows the total in calendar days, weeks, months, and years. Use Include end date when you need to count both the first and last day useful for event duration and legal periods.
Counting Business Days Between Two Dates
Check Business days only before calculating. The calculator skips all Saturdays, Sundays, and US federal holidays in the date range. Use Exclude weekends if you want to skip weekends but keep holidays. Both the calendar day count and the business day count appear side by side in the result.
Adding Days, Weeks, Months, or Years to a Date
Switch to the Add / Subtract tab. Select your starting date, enter an amount, choose the unit (days, weeks, months, years), and pick Add. The result shows the new date, the day of the week, and how far that date is from today. Month addition automatically adjusts the day when the target month is shorter.
Subtracting Days from a Date
In the Add / Subtract tab, change the operation to Subtract. This lets you find a date in the past useful for calculating deadlines working backward, finding when a warranty or subscription started, or identifying a date a fixed number of days before an event.
Using Countdown Mode
In the Date Difference tab, check Show countdown to end date. When the end date is in the future, the result card shows a live countdown days, weeks, and months remaining until that date. This is useful for event planning, exam countdowns, and project deadlines.
When People Use a Date Calculator
Professional Uses
- Project management: Calculate sprint lengths and milestone gaps
- Legal deadlines: Count business days for filing periods
- Finance: Find payment due dates and loan maturity dates
- HR: Track probation periods, notice periods, contract end dates
- Compliance: Confirm 30/60/90-day regulatory windows
Personal Uses
- Events & travel: Days until a vacation, wedding, or flight
- Anniversaries: Exact years and days since a milestone date
- Subscriptions: When does a 30-day free trial end?
- Warranties: Is my 2-year warranty still active?
- Study plans: How many days until the exam?
How Date Calculations Work
Calendar arithmetic is more complex than simple number arithmetic because months have different lengths, leap years add a day, and business day rules vary. Here is how each calculation type is handled.
| Calculation | Method | Edge Cases Handled |
|---|---|---|
| Calendar days | Counts every day from start to end | Leap years, varying month lengths |
| Business days | Skips weekends and US federal holidays | Holiday list built for the current year |
| Weekends only | Skips Saturday and Sunday, keeps holidays | Correct across month and year boundaries |
| Add months | Advances the month counter, adjusts day if target month is short | Jan 31 + 1 mo → Feb 28 or 29, not Mar 1 |
| Add years | Advances the year counter | Feb 29 + 1 year → Feb 28 in non-leap year |
| Include end date | Adds 1 to the calendar or business day total | Used for inclusive event durations |
Common Mistakes to Avoid
Forgetting to include the end date
By default the calculator counts up to but not including the end date. For event durations where both the first and last day count such as a 3-day conference on the 1st, 2nd, and 3rd check Include end date.
Confusing calendar days with business days
A 30-calendar-day period contains roughly 21 business days. Make sure you choose the right mode for your context legal contracts often specify calendar days while project timelines use business days.
Expecting month addition to always land on the same day
Adding one month to January 31 cannot land on February 31 that date does not exist. The calculator adjusts to the last valid day in February instead of jumping to March.
Not accounting for leap years
February has 29 days in a leap year. A date like February 29 + 1 year becomes February 28 in a non-leap year. The calculator handles this automatically, but be aware when comparing results year over year.
Using the wrong start point
When calculating a deadline that is 30 business days from today, start from tomorrow not today if today is not counted as Day 1 in your agreement or process.
Tips for Accurate Date Calculations
- Use the calendar picker to avoid typing errors in dates
- Check Show Full Breakdown to see years, months, weeks, and days all at once
- For legal or financial deadlines, confirm whether the agreement specifies calendar or business days
- Use Countdown mode to pin a future event date and track days remaining
- The Quick Calculations sidebar lets you jump straight to common periods like +30 days or +1 year
How the Calculator Works
All date arithmetic uses the date-fns library, which operates on the proleptic Gregorian calendar. Differences are computed in whole days first, then decomposed into years, months, weeks, and remaining days. Business day counting iterates day by day, skipping weekends and comparing each date against a list of holidays built for the current year. Month and year additions use date-fns's built-in overflow handling to prevent invalid dates.
Frequently Asked Questions
Calculate Any Date Instantly
Whether you need the number of days between two dates, the exact date 90 days from today, or a business-day count for a legal deadline, this free date calculator gives you an accurate answer immediately. Both tabs work in your browser with no login or installation required. Results expand into every time unit with one click, and the countdown mode keeps you on top of upcoming deadlines automatically.