Pregnancy Due Date Calculator
Estimate your due date from your last period, conception date, or ultrasound — with a full trimester breakdown and key milestone dates.
This is an estimate based on standard obstetric formulas (Naegele's Rule for LMP, or standard conception-date and ultrasound-based dating). It is not a substitute for advice, diagnosis, or care from a doctor or midwife.
How to Estimate Your Due Date
- Choose a calculation method: last menstrual period (LMP), conception date, or ultrasound-estimated gestational age.
- Enter the requested date(s) — for LMP, adjust the "Average Cycle Length" field if it isn't 28 days; for ultrasound, enter the gestational age your exam reported.
- Your estimated due date appears automatically, calculated using the standard day-count formula for that method.
- Your current gestational age, trimester, trimester date ranges, and key milestone dates are calculated from today's date.
Frequently Asked Questions
How accurate is this estimate?
It's a standard estimate based on Naegele's Rule (LMP plus 280 days), which is the same method most healthcare providers use for an initial due date. Only about 1 in 20 babies are actually born on their exact due date, so treat this as a helpful estimate, not a guarantee.
What if my cycle isn't 28 days?
Naegele's Rule assumes a 28-day cycle. If your average cycle is longer or shorter, enter your actual cycle length and the calculator adjusts the due date by adding the difference between your cycle length and 28 days.
What is Naegele's Rule?
It's a standard obstetric formula that estimates a due date as 280 days (40 weeks) from the first day of your last menstrual period, assuming a typical 28-day cycle and ovulation around day 14.
Why does the calculator show gestational age in weeks and days?
Pregnancy is conventionally tracked in weeks and days starting from the first day of your last period, not from conception, so gestational age is calculated as the number of days between your LMP and today, shown as weeks and remaining days.
Is this a substitute for medical advice?
No — this tool provides a mathematical estimate based on a standard formula. It is not a substitute for advice, diagnosis, or care from a doctor or midwife, who can confirm your due date with an ultrasound and adjust it based on your individual pregnancy.
What calculation methods does this tool support?
You can estimate your due date three ways: from the first day of your last menstrual period (Naegele's Rule: LMP + 280 days), from a known conception date (conception + 266 days), or from an ultrasound-estimated gestational age on a given exam date. All three methods estimate the same underlying due date using standard day-count formulas.
How is the trimester breakdown calculated?
The trimester breakdown shows the date ranges for each of the three trimesters based on your estimated pregnancy start date: roughly weeks 1-13 (first trimester), weeks 14-27 (second trimester), and weeks 28 through your due date (third trimester). Your current trimester is marked so you can see where you are today.
What do the milestone dates mean?
The milestones shown — end of first trimester (~13 weeks), viability (~24 weeks), and full term (~37 weeks) — are commonly-cited general reference points used in pregnancy tracking, not medical guidance. Your doctor or midwife may use different thresholds based on your individual pregnancy.