Date Calculator
Add or subtract days, weeks, months, or years to any date to find a past or future date.
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How to use this calculator
- 1
Select your start date using the date picker.
- 2
Choose whether to add or subtract time.
- 3
Enter the amount and select the unit (days, weeks, months, or years).
- 4
The resulting date appears instantly with the day of the week.
Frequently asked questions
Can I add years, months and days in one go?
No, each run takes one amount and one unit. To add 1 year and 3 months, run it twice, feeding the first result back in as the start date, or add 15 months in a single run.
What happens when I add a month to the 29th, 30th or 31st?
If the target month is too short, the result is clamped to its last day instead of spilling into the next month. January 31, 2026 plus 1 month is February 28, 2026; January 31, 2024 plus 1 month is February 29, 2024.
Does adding one year to February 29 land on March 1?
No, it lands on February 28 in a common year. February 29, 2024 plus 1 year gives February 28, 2025. If your contract or law treats leap-day anniversaries as March 1, adjust the result by one day.
Is subtracting the exact reverse of adding?
Not at month-end. March 31 minus 1 month gives February 28, but February 28 plus 1 month gives March 28, not March 31. Clamping loses the original day of the month, so do not assume a round trip returns to the start.
How does it handle decimals and negative amounts?
The amount is rounded down to a whole number and its sign is ignored; the Add/Subtract selector decides the direction. Entering −5 days with Subtract still moves back 5 days, and 2.8 days moves forward 2. A non-numeric amount returns a dash instead of a date.
What does the “Calendar days” line mean?
It is the number of days between the start date and the result, regardless of unit. Adding 1 month to January 31, 2026 shows 28 days, while the same step from January 31, 2024 shows 29, which makes the varying month length visible.
Does it skip weekends or holidays?
No, it moves through the calendar day by day. To move a date by working days instead, use the business days calculator, which skips Saturdays and Sundays but not public holidays.
Date calculator — add or subtract days, weeks, months and years
Why months and years are not fixed lengths
Days and weeks are constant, so adding 90 days is simple multiplication. Months and years are not: a month is 28 to 31 days and a year is 365 or 366. Adding a month therefore means keeping the day-of-month and changing the month, and the interesting question is what to do when that day does not exist. This calculator pulls the result back to the last day of the shorter month.
Worked examples
Every row below was produced by running the calculator.
| Start | Change | Result | Weekday |
|---|---|---|---|
| 2026-01-31 | +1 month | February 28, 2026 | Saturday |
| 2024-01-31 | +1 month | February 29, 2024 | Thursday |
| 2026-03-31 | −1 month | February 28, 2026 | Saturday |
| 2024-02-29 | +1 year | February 28, 2025 | Friday |
| 2026-11-03 | +90 days | February 1, 2027 | Monday |
| 2026-11-03 | −6 weeks | September 22, 2026 | Tuesday |
| 2026-01-15 | +18 months | July 15, 2027 | Thursday |
Month-end clamping and round trips
Because the day of month is clamped, adding and subtracting are not perfect inverses. Start on March 31 and subtract a month and you reach February 28; add a month to that and you reach March 28, three days short of where you began. When a deadline is defined as “the same date next month”, work from the original date each time rather than chaining results.
Choosing days, weeks or months for deadlines
A 90-day period and a three-month period are different things. From November 3, 2026, 90 days ends on February 1, 2027, while three months ends on February 3, 2027. Read the clause: wording in days is exact arithmetic, wording in months follows the calendar. The result also shows the weekday, which is worth checking before you commit to a date that falls on a weekend. Subscription renewals, warranty ends and lease breaks are usually written in months or years, while return windows and payment terms are usually written in days, so match the unit to the wording of the original document.
What it does not do
Only one amount and one unit are applied per run, there is no time of day, and weekends and public holidays are not skipped. For weekday-only arithmetic use the business days calculator. A blank or non-numeric date returns a dash rather than a guess, and a blank amount is read as zero, so the start date comes back unchanged.
Learn more from an authoritative source:
WikipediaDate Difference Calculator
Find the exact number of days, weeks, months, and years between two dates.
Time Calculator
Add or subtract two time values in hours, minutes, and seconds.
Working Days Calculator
Count the number of working days (Monday–Friday) between two dates, excluding weekends.
Business Days Calculator
Calculate a future or past date by adding or subtracting a number of business days (Mon–Fri).
Birthday Calculator
Discover your age, the day you were born, days until your next birthday, and your zodiac sign.
Retirement Calculator
Find out when you can retire based on your date of birth and target retirement age.
Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →