Date Calculator
Add or subtract days, weeks, months and years from any date. See the resulting date, weekday, ISO week and calendar-day shift instantly.
Add or subtract from a date
Combine years, months, weeks and days in one calculation.
Add or subtract days, weeks, months and years from a date
Use this date calculator when you know a starting date and want to move forward or backward by a calendar amount. You can combine years, months, weeks and days in the same calculation instead of doing each step separately.
The result includes the final calendar date, weekday, ISO week number, day of year and the total calendar-day shift from the starting date. The main inputs are also reflected in the URL so a calculation can be copied or shared.
Typical questions this calculator answers
Examples include “What date is 30 days from today?”, “What date is 12 weeks after March 1?”, “What was the date 6 months ago?” and “What date is 1 year, 2 months and 10 days after this date?”
How calendar date math works here
DateTimeWise applies calendar units from larger to smaller: years first, then months, then weeks and days. Years and months use calendar-aware arithmetic rather than treating every month as a fixed number of days.
Month-end dates are clamped to a valid date
If the destination month does not contain the original day number, the calculator uses the last valid day of that month. For example, adding one month to January 31 lands at the end of February rather than overflowing into March.
Weeks are exactly seven calendar days
One week is treated as seven days. If you need weekdays only, weekends excluded, or holiday exclusions, use the Business Days Calculator instead.
Calendar months are not the same as 30 days
Adding one month and adding 30 days can produce different results because months have 28, 29, 30 or 31 days. Choose the unit that matches the rule you actually need.
Worked date examples
| Start | Operation | What to expect |
|---|---|---|
| January 15 | + 30 days | A fixed 30-calendar-day shift |
| January 31 | + 1 month | The last valid day of February |
| March 1 | + 12 weeks | 84 calendar days later |
| Any date | − 1 year | The same month/day where valid, with leap-day handling |
For a fixed count between two existing dates, use Days Between Dates. For a human calendar difference such as “2 years, 3 months, 5 days,” use the Date Difference Calculator.
Common uses for date addition and subtraction
Deadlines and milestones: calculate a date a fixed number of days or weeks before or after a starting point.
Renewals and notice periods: move by calendar months or years when the rule is based on calendar units rather than a fixed day count.
Study, travel and project planning: turn a duration such as 8 weeks or 90 days into an exact calendar date.
Reference checks: see the weekday and ISO week of the calculated result without opening a separate calendar.
Date calculator FAQ
Does the calculator handle leap years?
Yes. Calendar arithmetic accounts for leap years, including February 29 where applicable.
Is one month always 30 days?
No. A calendar month keeps its actual length. Use the Days field if you specifically need a fixed number of calendar days.
What happens when I add one month to the 31st?
If the destination month has fewer days, the result is clamped to that month's last valid date.
Can I add years, months, weeks and days together?
Yes. The calculator applies years, then months, then the combined week-and-day amount.
Should I use this for business-day deadlines?
Not if weekends or holidays must be excluded. Use the Business Days Calculator for working-day rules.
For the exact conventions used by DateTimeWise, read How DateTimeWise Calculations Work.