Due Date Calculator
Calculate Due Date adds 280 days to the first day of the last period, then shifts that date by how far the cycle length sits from 28.
How to use
- Enter First day of last period (LMP).
- Enter Cycle length (days). The field starts at 28, with a minimum of 20 and a maximum of 45. If it is left blank, the math uses 28.
- Click Calculate Due Date. The result is the due date. The detail line writes that date in words and, when the rules below allow it, adds an approximate week.
When it helps
The due date is LMP plus 280 plus (cycle minus 28). A 28-day cycle adds nothing extra. A 30-day cycle adds two days. A 26-day cycle subtracts two. That difference from 28 is the whole adjustment.
The pregnancy calculator always uses 280 days, names the trimester, and rejects a future LMP. If you need the number of days between the due date and another calendar day, the date calculator compares two dates or adds and subtracts days.
Limits
The printed due date is an estimate from the cycle length you typed, not a diagnosis. It is not an ultrasound date, and it does not know a later clinical revision.
An approximate week is shown only when the LMP is not in the future and the week count is within 42 weeks. A future LMP still produces a due date on this page, but the week is omitted. An empty LMP says Enter LMP date. The week line is not a trimester name.
Questions
How does cycle length change the date?
Due date equals LMP plus 280 plus (cycle minus 28). Only the gap from 28 days moves the result.
Why is the week sometimes missing?
The approximate week is added only if the LMP is not in the future and the count is within 42 weeks. You still get the due date.
Is this the same due date as the pregnancy page?
Only when cycle length is 28. Any other length shifts the date. The pregnancy page has no cycle field and always adds 280 days.