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Date Calculator: Add or Subtract Days
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Add or subtract years, months, weeks, and days from a specific date to quickly calculate your target date.
Result Date
Lunar：2026年十月十五
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
Enter a starting date, choose Add or Subtract, enter a number, and select days, weeks, months, or years. The result shows a calendar date and weekday; a corresponding lunar date may also appear. This answers date arithmetic questions such as “What date is 45 days after September 19?” It does not find the number of days between two dates.
Days move by calendar days, and one week is seven days. Months and years move calendar fields rather than using a fixed number of days. That distinction matters because months have different lengths and leap years add February 29. In the Gregorian calendar used for ordinary civil dates, a year divisible by four is a leap year except a century year, which must be divisible by 400.
Days: result = start date ± n calendar days
Weeks: result = start date ± (7 × n) calendar days
Months or years: move the corresponding calendar field and allow an invalid day number to roll into the following month.
For example, adding one month to January 31, 2026 produces March 3, because February has no 31st and the extra days roll forward. Adding 30 days to that same date produces March 2. A month is therefore not interchangeable with 30 days.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Check the prefilled date or select the date the calculation should begin from. The picker also offers a lunar calendar selection mode; the chosen day is used as the starting date for the arithmetic.
Select Add to move forward or Subtract to move backward. Enter the number and choose exactly one unit: days, weeks, months, or years. The displayed result updates as you change the inputs.
Use the main date for the target day and the weekday as a quick scheduling check. If shown, the lunar date is an additional calendar label. The reset control restores the current date, Add, 30, and days, so verify the fields after resetting.
Example: Starting September 19, 2026, adding 2 weeks moves forward 14 calendar days to October 3, 2026. The start date is the zero point; adding one day means the following date.
Use cases
See how the tool fits into real work and everyday tasks.
A coordinator given a “30 calendar days after kickoff” milestone can enter the kickoff date and add 30 days, then use the weekday to place the checkpoint on a team calendar.
If materials should be ready three weeks before a planned submission, enter the submission date, subtract three weeks, and use the result as a planning date.
For a reminder a year after a selected date, add one year and check the result around a leap day or month end before saving it.
Q&A
Find concise answers to common questions and confusing cases.
The calculation moves the month field while retaining the day number. When the target month lacks that day, the extra days roll forward; January 31, 2026 plus one month becomes March 3, 2026. It does not clamp the result to February’s last day.
No. The starting date is the offset origin, so adding one day returns the next calendar date. If a rule counts the start date as its first numbered day, account for that rule separately.
No. Each calculation uses one amount and one unit. To combine intervals, calculate one part, use that result as the next starting date, and apply the next part. Around month ends, the order can change the outcome.
Notes
Review scope, result limitations, and important precautions before use.
This is a calendar-date offset. It does not count business days, remove weekends or holidays, determine a legal deadline, or calculate a duration between two dates. It also does not calculate a time of day or time-zone conversion.
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