Pregnancy Due Date Calculator
Use this tool to estimate your due date, current gestational age, and trimester. You can calculate from your last menstrual period (LMP) or from a known conception date.
Note: This estimate uses standard obstetric dating (about 40 weeks from LMP or 38 weeks from conception). Your healthcare provider may adjust dates based on ultrasound and clinical findings.
How this pregnancy calculator works
If you searched for a pregnancy calculator American Pregnancy Association style tool, you are likely trying to answer one key question: “When is my baby due?” This calculator follows the same common medical dating principles used in many online due date tools.
There are two standard ways to estimate due date:
- From LMP: Add 280 days (40 weeks) to the first day of your last menstrual period, with a small adjustment for cycle length.
- From conception: Add 266 days (38 weeks) to your conception date.
What you get in your results
After calculation, the tool gives you a practical snapshot you can discuss with your OB-GYN or midwife:
- Estimated due date (EDD)
- Estimated conception date (or estimated LMP when calculating from conception)
- Current gestational age in weeks and days
- Current trimester (first, second, or third)
Step-by-step: using the calculator accurately
1) Pick the right method
Choose LMP if you know the first day of your last period. Choose Conception Date if conception timing is known (for example, with ovulation tracking or fertility treatment).
2) Enter realistic cycle length
If your cycle is not 28 days, update that number. Longer cycles often shift ovulation later, which can move your due date slightly.
3) Treat the result as an estimate
Even with precise inputs, a due date is a target window. Most births happen within a range around the estimated due date, not exactly on that day.
Understanding pregnancy dating in plain language
Why pregnancy weeks start before conception
Medical dating usually starts from LMP, not conception. That means “2 weeks pregnant” is often around the time ovulation and fertilization may occur.
Trimester timing
- First trimester: Week 1 through week 13
- Second trimester: Week 14 through week 27
- Third trimester: Week 28 to birth
When dates can change
Early ultrasound can revise due date, especially if your cycles are irregular or your LMP is uncertain. Your provider’s charted due date is the one to follow for medical decisions.
Common reasons estimates may differ
- Irregular menstrual cycles
- Uncertain or forgotten LMP
- Late or early ovulation
- Recent hormonal contraception use
- Date adjustment after first-trimester ultrasound
Frequently asked questions
Is this calculator affiliated with the American Pregnancy Association?
No. This page is an independent educational replica-style resource and is not an official American Pregnancy Association page.
Can I rely on this for medical decisions?
Use it for planning and education only. Confirm all dates and care milestones with a licensed healthcare professional.
Why does my ultrasound due date not match this result exactly?
That is common. Ultrasound-based dating, especially in early pregnancy, may be more accurate than menstrual dating.
Helpful planning checklist after calculating your due date
- Schedule or confirm your first prenatal appointment
- Start or continue prenatal vitamins (as advised)
- Track symptoms, questions, and medications for your visit
- Ask your provider which due date should be used going forward
- Discuss nutrition, activity, and warning signs that need urgent care