How to use the due date calculator
- Enter the first day of last menstrual period (LMP).
- Set As of date (usually today) for current gestational age.
- Read estimated due date, weeks and days pregnant, and days since LMP.
- Copy link to save LMP and as-of date—not a medical record.
Example: LMP and 280-day rule
LMP January 1 → estimated due date about 280 calendar days later (40 weeks). As of any date between LMP and due date, gestational age shows as weeks + days (e.g. 12 weeks 3 days). Clinics often adjust dating after ultrasound; treat this as planning math only.
LMP due date vs. other date tools
Due date is a fixed LMP + offset problem—same engine as add/subtract date with 280 days. Countdown to due date with days until. For a parent’s age, use the age calculator.
Frequently asked questions
How is due date calculated from last period (LMP)?
Enter LMP day 1; this page uses LMP + 280 days. Your clinician may adjust.
How many weeks pregnant am I from my LMP?
Enter LMP and as-of date (often today)—gestational weeks + days appear in the results panel.
Why add 280 days?
Common 40-week (280-day) rule from the first day of LMP.
Why doesn’t this match my ultrasound weeks?
Ultrasound uses fetal measurements; this page uses LMP calendar math—follow your provider.
Can I change the as-of date?
Yes—update as-of to see gestational age on that day and days since LMP.
How many days until my due date?
For a countdown, use the days until calculator from today to your due date.
Is this medical advice?
No. Confirm dates and care with a qualified clinician.
What if I do not remember my LMP?
Use records from your provider; this tool cannot replace ultrasound dating.
Can I share my dates?
Copy link saves LMP and as-of date in the URL.