Add or Subtract Dates
Calculate a future or past date by adding or subtracting years, months, weeks, and days.
How to use the date calculator
This tool lets you add or subtract any combination of years, months, weeks, and days from a starting date. Say whether you know your start date or your end date, pick it with the calendar picker, choose whether to add or subtract, enter the number of each time unit you want, and click Calculate. The result shows the exact target date formatted in a readable way.
Common uses for adding and subtracting dates
- Project deadlines: Add 90 days to a project start date to find the target completion date.
- Contract end dates: Add 12 months or 1 year to a signing date to find when a contract expires.
- Countdown planning: Subtract 30 days from an event date to set a reminder deadline.
- Deadline start dates: Know your end date, subtract the time the task takes, and the calculator works out the day you need to start.
- Age milestones: Add 18 years to a birth date to find the legal adulthood date.
- Retirement planning: Add years to your current age to project your retirement date.
- Historical research: Subtract years from the current date to find what date was X years ago.
How leap years are handled
The calculator automatically accounts for leap years. If your calculation spans a February 29 (a leap day), the result will be accurate. For example, adding 1 year to February 28, 2024 will return February 28, 2025 (not March 1), because the leap day in 2024 is properly handled. The underlying date library (date-fns) handles all edge cases including month-length variations and leap year rules.
Popular date calculations, worked out
These are the calculations people run most often this season, with the exact answers. Use the calculator above for any other combination.
30, 60, and 90 days from a date
Thirty-day and ninety-day windows are the workhorses of deadline planning — visa applications, return windows, notice periods, probation periods, and project sprints. The table below starts from the first of each remaining 2026 month so you can eyeball your window.
| Start date | +30 days | +60 days | +90 days |
|---|---|---|---|
| September 1, 2026 | October 1, 2026 | October 31, 2026 | November 30, 2026 |
| October 1, 2026 | October 31, 2026 | November 30, 2026 | December 30, 2026 |
| November 1, 2026 | December 1, 2026 | December 31, 2026 | January 30, 2027 |
| December 1, 2026 | December 31, 2026 | January 30, 2027 | March 1, 2027 |
| December 25, 2026 | January 24, 2027 | February 23, 2027 | March 25, 2027 |
A note on the phrase "90 days": in legal and immigration contexts, it can mean calendar days(90 days on the calendar — the figure above) or business days (weekdays excluding weekends, roughly 18 weeks ≈ 126 calendar days). Contracts usually specify; when they don't, assume calendar days unless a statute says otherwise.
"From today" answers, month by month
"X months from today" queries spike around planning season. Six months from September 11, 2026 is March 11, 2027; 18 months from today is March 11, 2028. The pattern to remember: adding months keeps the day-of-month when possible, clamping to the month's end when it isn't — six months from August 31 lands on February 28/29, not March 2 or 3.
Why 90 days and 3 months are not the same thing
Ninety days from September 1, 2026 is November 30, 2026. Three months from September 1 is December 1, 2026 — one day more, because the three months the span crosses (September, October, November) add up to 30+31+30 = 91 days. Month arithmetic counts months; day arithmetic counts days, and the two only align by coincidence. This is the single most common deadline-planning mistake, and it usually costs exactly one day.
Business days: the 30/5/6 rule of thumb
Ten business days ≈ 14 calendar days. Twenty business days ≈ 28 calendar days (almost a month). The exact answer depends on where weekends and holidays fall — use the calculator with the month-by-month table above to sanity-check any "business days" deadline. For precise business-day math including U.S. federal holidays, see our federal holidays 2026–2027 table.
What about leap years?
The calculator handles February 29 automatically (2028 is the next leap year). Adding one year to February 29, 2028 returns February 28, 2029 — the day is clamped to the end of the shorter month rather than rolling into March.
Related tools
- Date Duration Calculator — find the time between two dates.
- Week Number Calculator — find the ISO week number.
- Age Calculator — calculate your exact age.
- Calendar Generator — create and print a yearly calendar.
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Frequently Asked Questions
A Date Adder/Subtractor is a tool that calculates a future or past date by adding or subtracting a specific duration (years, months, weeks, days) from a given start date. It automates complex date math.
First, choose whether you know your 'Start date' or your 'End date'. Second, select that date. Third, choose an 'Operation' (Add or Subtract) and enter the number of years, months, weeks, or days. Finally, click 'Calculate New Date' to see the result.
Yes. Switch 'I know my' to 'End date', pick your deadline, then choose 'Subtract' and enter the time you need. For example, an end date of December 25 with 30 days subtracted shows November 25 as the date to start on. This is the usual way to plan backwards from a deadline, a launch date, or an event.
No, you must choose one operation, either 'add' or 'subtract', for a single calculation. You can, however, combine different units, such as adding 1 year and 6 months simultaneously.
The calculator's underlying date logic automatically accounts for leap years. When you add or subtract a duration that crosses February 29th in a leap year, the tool includes that extra day for an accurate result.
Displaying the day of the week (e.g., Monday, Tuesday) for the resulting date provides extra context, which is very useful for planning events or scheduling appointments.
The input fields are designed for practical calculations, typically within a few hundred years. There are no hard limits, but extremely large numbers may not be practical.
Yes. Set the 'Start Date' to today, select the 'Add' operation, enter 90 in the 'Days' field, and leave the other duration fields as 0. The tool will give you the exact date.
Our calculator is designed for CE (Common Era) dates and may not provide accurate results for dates before 1 AD. It's best used for modern and recent historical date calculations.
No, the duration fields (years, months, etc.) only accept positive integers. The 'Subtract' operation is used to calculate past dates.
This error appears if all duration fields (years, months, weeks, and days) are set to zero. You must enter a value greater than 0 in at least one of these fields to perform a calculation.
No, this is a standard date calculator and does not exclude weekends or public holidays. It calculates based on calendar days only.
Yes. Enter your birth date as the 'Start Date', select 'Add', enter 10,000 in the 'Days' field, and the calculator will show you the exact date of this unique milestone.
It's faster, more accurate, and eliminates human error. The tool automatically handles the different number of days in each month and leap years, which is difficult to do manually.
Yes. After you get a result, click the 'Share' button. This copies a unique URL to your clipboard that you can send to others, and they will see the same calculation you performed.
No, all calculations are performed in your browser. We do not store any of the dates or durations you enter, ensuring your privacy.
The calculator defaults to using today's date as the start date, making it easy to quickly calculate a date in the future or past from now.
Yes, if the loan term is specified in years, months, or days. For example, you can easily find the end date of a 5-year loan by adding 5 years to its start date.
The calculations are based on dates only and are independent of time zones. The 'Start Date' is treated as a full day.
Adding 4 weeks will always result in a date exactly 28 days later. Adding 1 month will result in the same date in the next month, which could be 28, 29, 30, or 31 days later, depending on the month.
Simply change the values in the input fields and click the 'Calculate New Date' button again. The result will update instantly.