Pregnancy Calculator
Use this Pregnancy Calculator to estimate your due date, how many weeks pregnant you are, your trimester, likely conception window, and a more detailed pregnancy timeline. It is built to be educational, student friendly, and helpful for common pregnancy dating questions.
Background
Pregnancy is usually dated in gestational age, which counts from the first day of the last menstrual period (LMP), even though conception usually happens about 2 weeks later. Ultrasound in early pregnancy can sometimes refine the due date, which is why dating scans are often treated as more accurate than memory-based dating alone.
How to use this calculator
- Choose the pregnancy calculation mode that matches the information you know.
- Enter your date, such as LMP, conception date, IVF transfer date, a known due date, or an ultrasound date with gestational age.
- Click Calculate to see the estimated due date, pregnancy week, trimester, conception estimate, milestone timeline, and the development explorer.
How this calculator works
- For LMP mode, it starts from the first day of the last menstrual period and uses the standard pregnancy dating method.
- For conception mode, it adds about 266 days to the conception date to estimate the due date.
- For IVF mode, it uses the embryo transfer date and embryo age to estimate gestational age and the due date.
- For known due date mode, it works backward from the due date to estimate the current gestational age.
- For ultrasound mode, it uses the scan date plus the gestational age measured on that date to calculate the remaining time to 40 weeks.
Formulas & Rules Used
LMP due date: EDD = LMP + 280 days + (cycle length − 28 days)
Conception due date: EDD = conception date + 266 days
Ultrasound due date: EDD = scan date + (280 − gestational age on scan in days)
Gestational age from due date: gestational age in days = 280 − days until due date
Trimester ranges: 1st: 0–13 weeks 6 days, 2nd: 14–27 weeks 6 days, 3rd: 28 weeks to birth
Example Problems & Step-by-Step Solutions
Example 1 — Due date from LMP
- Start with the first day of the last menstrual period.
- Add 280 days.
- Adjust for cycle length if the average cycle is not 28 days.
- The result is the estimated due date.
Example 2 — Due date from conception
- Start with the estimated conception date.
- Add 266 days.
- The result is the estimated due date.
Example 3 — Due date from ultrasound
- Enter the ultrasound date.
- Enter the gestational age measured on that scan date.
- The calculator adds the remaining days needed to reach 280 gestational days.
Frequently Asked Questions
Q: How many weeks pregnant am I if I know my LMP?
Count forward from the first day of your last menstrual period. Pregnancy dating usually starts from that date, not from the day of conception.
Q: Can ultrasound change the due date?
Yes. In early pregnancy, ultrasound can refine the estimated due date and is often more accurate than dating based only on remembered period dates.
Q: Is a due date exact?
No. A due date is an estimate. Birth can happen before or after that date.
Q: Can I use this calculator instead of medical care?
No. This tool is educational. A clinician or ultrasound can provide more accurate dating and guidance.
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