Pregnancy Calculator
Enter the first day of the last menstrual period and the page reports week plus day, a trimester, and a due date 280 days after that LMP.
How to use
- Enter First day of LMP.
- Click Calculate.
- Read the result as Week, a plus sign, and the leftover days. The detail line names the trimester and the estimated due date.
When it helps
The count is whole days from the LMP through today, grouped as weeks plus leftover days. First trimester is before week 13. Second is before week 27. From week 27 on, the label is third. The due date is always the LMP plus 280 days.
If the cycle is not 28 days, the due date calculator shifts the date by cycle length minus 28. For one conception guess rather than a week count, the conception calculator adds 14 days to an LMP or counts backward from a due date.
Limits
Week, trimester, and due date are calendar estimates, not a diagnosis and not an ultrasound. The form assumes a 28-day cycle and has no place to type a different cycle length.
A future LMP is rejected and the result says LMP is in the future. An empty date says Enter LMP. The page does not know spotting versus a period, an IVF transfer date, or a date a clinician later revised.
Questions
What does the plus sign in the result mean?
It joins weeks and leftover days since the LMP. Week 12+3 means 12 weeks and 3 days, not a second score.
When does each trimester start?
Before week 13 is first. From week 13 until week 27 is second. Week 27 and later is third.
Will a longer cycle move this due date?
No. This due date is always LMP plus 280 days. The due date calculator is the page that applies a cycle length.