Pregnancy Due Date Calculator
Estimate your due date from your last menstrual period (LMP) or conception date. See your gestational age, trimester, and key milestones — free, no sign-up, nothing leaves your browser.
Not medical advice. This tool uses Naegele's rule and provides estimates only. Always consult your midwife, OB-GYN, or healthcare provider for personalised guidance and accurate dating via ultrasound.
Calculation method
How It Works
Choose a method
Select "Last Menstrual Period" to use the standard clinical method, or "Conception Date" if you know approximately when you ovulated.
Enter your date
Pick the relevant date from the calendar. For LMP, use the first day of your last period. Results appear the moment you select a date.
See your due date
Your estimated due date (EDD), gestational age in weeks and days, trimester, and days remaining are shown instantly.
Review milestones
Scroll the milestone timeline to see dates for key appointments — ultrasounds, viability, full term — with past milestones checked off.
What is a pregnancy due date?
Your estimated due date (EDD) is the date on which your baby is expected to be born — typically 40 weeks (280 days) after the first day of your last menstrual period. Only about 5% of babies arrive on their exact due date; most births occur within two weeks before or after. Your due date is a planning target, not a deadline.
How is the due date calculated? (Naegele's Rule)
This calculator uses Naegele's rule, the standard method used by obstetricians and midwives worldwide:
- Start from the first day of your last menstrual period (LMP).
- Add 1 year.
- Subtract 3 months.
- Add 7 days.
This is mathematically equivalent to adding 280 days (40 weeks) to your LMP, which is what this tool does. The formula assumes a 28-day cycle with ovulation on day 14. If your cycles are significantly longer or shorter, an ultrasound will give a more accurate date.
LMP vs. Conception Date
| Method | What you enter | How it works | Accuracy |
|---|---|---|---|
| LMP (Last Menstrual Period) | First day of last period | Adds 280 days | Standard clinical method — very good if cycles are regular |
| Conception Date | Approximate ovulation/conception date | Subtracts 14 days to estimate LMP, then adds 280 days | Good if you tracked ovulation or used OPKs |
| Early Ultrasound (not in this tool) | Performed by your provider | Measures fetal size against gestational age tables | Most accurate — gold standard before 13 weeks |
Pregnancy trimesters explained
- First trimester (weeks 1–12) — rapid embryonic development, highest risk of miscarriage, nausea and fatigue common.
- Second trimester (weeks 13–26) — often called the "honeymoon trimester"; energy returns, bump becomes visible, anatomy scan at ~20 weeks.
- Third trimester (weeks 27–40) — rapid fetal growth, preparation for birth, glucose testing and GBS screening.
Key pregnancy milestones
- Week 8 — first prenatal visit; heartbeat visible on ultrasound.
- Week 10 — NIPT (non-invasive prenatal testing) window opens for chromosomal screening.
- Week 12 — nuchal translucency (NT) scan; end of the highest-risk period.
- Week 20 — anatomy scan checks fetal organs and growth.
- Week 24 — viability milestone; survival outside the womb becomes possible with intensive care.
- Week 28 — third trimester begins; glucose tolerance test (GCT/OGTT).
- Week 36 — GBS (Group B Streptococcus) swab test.
- Week 37 — early full term; most providers comfortable with delivery if needed.
- Week 39–40 — full term; ideal delivery window.
Privacy
All calculations run entirely in your browser. The dates you enter are never transmitted to or stored on any server. This tool works fully offline after the page has loaded.
Frequently Asked Questions
How is my due date calculated?
This calculator uses Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). Your OB-GYN may adjust the date after an early ultrasound, which is considered the most accurate dating method before 13 weeks.
What is gestational age?
Gestational age is counted from the first day of your last menstrual period — not from conception. When your provider says you're '10 weeks pregnant', they mean 10 weeks of gestational age. A full-term pregnancy is 40 weeks.
What are the three trimesters?
The first trimester runs from week 1 through week 12. The second trimester covers weeks 13–26. The third trimester runs from week 27 to delivery (typically around week 40).
What if I don't know my LMP date?
If you know your approximate conception or ovulation date, switch to the 'Conception Date' method. The calculator subtracts 14 days to estimate your LMP and computes your due date from there. For the most accurate dating, ask your provider for an early ultrasound.
How accurate is this due date calculator?
Due dates based on LMP are estimates — only about 5% of babies arrive on their exact due date. Most births occur within two weeks before or after the EDD. An ultrasound before 13 weeks of gestation is significantly more accurate for confirming your due date.
When is full term?
Full term is 39 weeks 0 days through 40 weeks 6 days of gestational age. Early term is 37–38 weeks. Providers typically consider 37 weeks the threshold for a safe delivery, but the ideal window is 39–40 weeks.
Is my data stored or sent anywhere?
No. All calculations happen entirely in your browser using JavaScript. The dates you enter are never sent to or stored on any server — not even anonymously.
Privacy & Security
This tool is not a substitute for medical care. Always consult a qualified midwife, OB-GYN, or healthcare provider for personalised advice on your pregnancy.