January 31 + 1 month + 1 day
2024-01-31 → 2024-02-29 → 2024-03-01
February 2024 has 29 days. The month step first lands on February 29, then one day is added. The result is Friday, March 1, 30 calendar days after the start.
Time and planning
Date Calculator
Move forward or backward from a date by years, months, weeks, and days.
Add or subtract a date offset
Resulting date · YYYY-MM-DD
Enter a start date and offset, then select Calculate.
Calculation steps
Uses calendar dates, including weekends and public holidays. Your inputs are calculated in your browser.
Examples and calendar rules
January 10 − 2 weeks − 3 days
2025-01-10 − 17 days = 2024-12-24
Two weeks are 14 days. Subtracting those and another three days gives Tuesday, December 24. Weekends and holidays remain ordinary calendar days.
Leap day + 1 year + 1 month
2024-02-29 + 13 months = 2025-03-29
Years and months form one combined shift, so March 29 is valid and no adjustment is needed. This differs from doing two separate calculations that first shorten February 29 to February 28.
Order, limits, and exactness
The year/month shift is 12 × years + months. Move to that month in the chosen direction and keep the original day number if it exists; otherwise use that month's last day. Then move by 7 × weeks + days whole calendar days. Subtraction uses the same order with both shifts directed backward.
This rule does not preserve “last day of the month” as a special setting. April 30 plus one month is May 30. Month shifts are also not always reversible: January 31, 2024 plus one month becomes February 29; subtracting one month from that result gives January 29.
The proleptic Gregorian calendar is used throughout years 0001–9999, including dates before its historical adoption. A leap year is divisible by 4, except century years must also be divisible by 400. Thus 2000 is a leap year, while 1900 and 2100 are not. Calendar reference: U.S. Naval Observatory — Leap Years.
Individual quantity limits are 9,998 years, 119,987 months, 521,722 weeks, and 3,652,058 days. Their combined result must still stay within 0001-01-01 through 9999-12-31. If it would leave that range, the calculator reports an error rather than wrapping the year. All four quantity fields are required; use 0 for an unused unit.
Dates are counted as whole calendar days without timestamps, time zones, or daylight-saving adjustments. Results are exact for this calendar rule and need no decimal rounding. Zero added or subtracted days keeps the start date; one added day gives the next calendar date. Inclusive date-range counting is a separate option in the Date Difference Calculator.
Common questions
Is adding one month the same as adding 30 days?
No. Months have 28, 29, 30, or 31 days. For example, January 31, 2024 plus one month is February 29, but plus 30 days is March 1.
Does it skip weekends or public holidays?
No. These are calendar units. The weekday is shown so you can see where the result falls. For working-day offsets, use the Business Days Calculator with your weekend pattern and holiday list. Neither tool determines organization-specific deadline rules.
Why can adding and subtracting the same months give different dates?
A month-end adjustment can discard a day number that the target month does not contain. After January 31 becomes February 29, a new calculation starts with day 29. It no longer has the original day 31 to restore.
Can I add some units and subtract others together?
Each calculation has one direction for all units. For mixed directions, run separate calculations in the order you intend, using each result as the next start date. Month-end adjustments can make the order matter.