CloudCalcAppWhat the Date Calculator Does
The Date Calculator answers one question: which date do you reach if you add time to a start date, or take time away from it? You enter any mix of years, months, weeks and days, choose Add or Subtract, and it returns the resulting date, the day of the week it falls on, the same date in ISO format (year-month-day), and how many calendar days separate it from the start date.
It suits everyday planning: a due date, a renewal or expiry date, a follow-up date, or a past date such as the day something happened. The start date is set to today's date on your device when the page loads, so a date counted from today needs only the amount, and you can change the start date to any other day.
It adds and subtracts calendar time and nothing else: it does not skip weekends or holidays, and it does not count the days between two dates you choose. To find how old someone is, use the Age Calculator; the other tools are listed under Date & Time calculators.
How to Use the Date Calculator
- 1Check the start date. It is set to today's date on your device automatically; pick another date if you need a different starting point.
- 2Select Add or Subtract, then enter any mix of years, months, weeks and days. Leave unused boxes blank - a blank box counts as 0.
- 3Press Calculate Date to see the resulting date, its weekday, the number of calendar days between the two dates and the working step by step.
To count from today, leave the start date as it is. To count from a specific day, such as a purchase date or the date of a past event, change it first. The Clear button puts the start date back to today and empties everything else.
What Date Is 7, 30 or 90 Days From a Date?
To find a date a set number of days away, choose Add for a future date or Subtract for a past one, and enter the number in Days. Weeks work the same way, since one week is exactly seven days. Days are counted one at a time across month ends and leap days, so the answer does not depend on how long the months in between are.
Choose a duration to fill in the calculator above with today's date on your device and that many days, and see the result straight away.
How Months and Years Are Added
Months and years follow the calendar, not a fixed number of days. Adding one month to the 15th gives the 15th of the next month whatever length the months are: January 15, 2026 plus one month is February 15, 2026, which is 31 days later, whereas adding 30 days gives February 14, 2026. "One month" and "30 days" are different questions and often have different answers.
A year is added as 12 months, so the day and month stay the same and only the year changes, with one exception for February 29 covered below. Subtracting follows the same rules in the other direction.
When the day does not exist
Not every month has a 31st. If the new month is too short for the starting day, the calculator uses that month's last day instead. Adding one month to January 31 therefore gives February 28, 2023, or February 29, 2024 in a leap year. IBM's date documentation and the Java date library describe the same rule. Each row below starts again from the original date; it is not a chain of one-month steps.
| Months added | From January 31, 2023 | From January 31, 2024 |
|---|---|---|
| 1 | February 28, 2023 (moved to month end) | February 29, 2024 (moved to month end) |
| 2 | March 31, 2023 | March 31, 2024 |
| 3 | April 30, 2023 (moved to month end) | April 30, 2024 (moved to month end) |
| 4 | May 31, 2023 | May 31, 2024 |
Subtracting months
The same rule applies going backward. Subtracting one month from March 31, 2024 gives February 29, 2024, because February has no 31st, and subtracting two months gives January 31, 2024.
Leap Years and Month-End Adjustments
A year is a leap year when it divides by 4, except that century years must divide by 400. That makes 2024 and 2000 leap years and 1900 and 2100 ordinary years. A leap year has a February 29, and the extra day changes an answer only when a calculation crosses the end of February.
| Year | Leap year? | February 28 plus 1 day |
|---|---|---|
| 2023 | No | March 1, 2023 |
| 2024 | Yes | February 29, 2024 |
| 1900 | No | March 1, 1900 |
| 2000 | Yes | February 29, 2000 |
| 2100 | No | March 1, 2100 |
A leap day as the start date. February 29, 2024 plus 1 year is February 28, 2025, because that year has no February 29. Plus 4 years it is February 29, 2028. The adjustment is applied once, to the combined months, not year by year.
A month-end adjustment loses the original day number, so adding and then subtracting the same amount may not bring you back to where you started. May 31, 2025 minus one month is April 30, 2025, but adding one month to that gives May 30, 2025, not the 31st. The result panel flags every adjustment it makes.
Adding Years, Months, Weeks and Days Together
When you fill in more than one box, years and months are combined first (years × 12 + months) and applied in one step. Weeks and days are then combined (weeks × 7 + days) and counted from the date that step produced. Subtract uses the same order.
Worked example. Start from Sunday, November 30, 2025 and add 3 months, 2 weeks and 4 days. Three months on lands in February, which has no 30th, so the date moves to that month's last day, February 28, 2026. Two weeks and 4 days make 18 days, and February 28, 2026 plus 18 days is Wednesday, March 18, 2026, a gap of 108 calendar days from the start.
The order matters near a month end. For February 28, 2023, adding 1 month and then 1 day gives March 29, 2023; applying the day first gives April 1, 2023. The calculator always applies months first and shows the intermediate date in its step-by-step working, so you can see exactly which date it used.
Calendar Days, Weekends and Business Days
The calculator counts calendar days: every day in the span, including Saturdays, Sundays and public holidays. Thirty days from January 15, 2026 lands on Saturday, February 14, 2026, and the calculator reports exactly that. It shows the weekday but never shifts the date to a weekday.
If a date has to fall on a working day, read the weekday in the result and adjust it by whatever rule applies to you, such as the next or the previous business day. Which days count as non-working depends on the country, the employer or the contract, so the calculator does not guess. Counting only working days is a different calculation from adding calendar days.
Why Two Date Calculators Can Show Different Results
With identical inputs, calculators can still return different dates. timeanddate.com's own help page says there is no perfect way to calculate dates that include months and years, so the convention behind a tool matters. The usual reasons are:
- Month ends. This calculator moves to the last day of a short month. A tool that carries the extra days into the next month turns January 31, 2023 plus one month into March 3, 2023.
- Order of units. Applying days before months, or adding months one at a time, can change the result near a month end (see the combined example above).
- The start day. Some tools and some deadline wordings count the start day as day 1, which gives a date one day earlier. This calculator counts the first day after the start date as day 1.
- Fixed-length months. A calculator that treats every month as 30 days and every year as 365 drifts away from the calendar.
- What "today" means. Today depends on the time zone of the device. Near midnight, two people in different time zones can honestly be on different dates.
Common Mistakes When Calculating Dates
Counting the start day twice
If a form says "within 30 days of" a date, check whether that date is day 0 or day 1 before relying on any calculator, including this one. A one-day difference can decide whether a deadline is met.
Adding months one at a time
Adding one month three times is not the same as adding three months once. From January 31, 2023, three single steps go February 28, 2023, March 28, 2023, April 28, 2023, while adding three months in one step gives April 30, 2023, because the first short month cost the chain its original day number.
Relying on very old dates
Dates before October 15, 1582 are shown in the proleptic Gregorian calendar, which applies today's leap-year rules backward. Many places were still on the Julian calendar then, so a date taken from an old record can differ from the one this calculator shows.
This calculator does the calendar arithmetic only. It is not legal advice: contracts, courts and agencies can set their own counting rules, for example by excluding the first day or counting only business days, so confirm the rule that applies to you.