Pregnancy Due Date Calculator
Calculate your estimated due date from your last period, conception date, or IVF transfer date.
How to use this calculator
Choose your calculation method. For LMP (most common): enter the first day of your last menstrual period and your average cycle length (default is 28 days). For conception date: enter the date you believe conception occurred. For IVF: enter your transfer date and select whether a 3-day or 5-day embryo was transferred. Your due date and pregnancy milestones will appear instantly.
Understanding your due date
The estimated due date (EDD) is calculated using Naegele's rule — the standard medical formula used by OBs worldwide. Only about 5% of babies are born on their exact due date. A "term" pregnancy is 37-42 weeks, and birth is normal throughout this range. Your gestational age is counted from the first day of your last period, not from conception — which is why pregnancy is described as 40 weeks even though conception happens around week 2.
Frequently asked questions
Pregnancy timeline — key milestones by week
Pregnancy is divided into three trimesters, each with distinct developmental milestones. Gestational age is counted from the first day of the last menstrual period (LMP), not from conception.
| Week | Trimester | Key development |
|---|---|---|
| Weeks 1–4 | First | Fertilization, implantation; pregnancy test positive by week 4 |
| Weeks 5–8 | First | Heart beating by week 6; major organs forming; morning sickness peaks |
| Weeks 9–12 | First | Fingers, toes forming; fetus moves; end-of-trimester ultrasound common |
| Weeks 13–16 | Second | Second trimester begins; energy returns; anatomy scan scheduled |
| Weeks 18–20 | Second | Anatomy ultrasound (sex can be determined); baby kicks felt |
| Weeks 24–28 | Second | Viable outside womb (with intensive care) from week 24; glucose test |
| Weeks 28–32 | Third | Rapid brain development; GBS testing; baby gains weight fast |
| Weeks 37–40 | Third (term) | Full term; lungs mature; birth expected anytime in this window |
How due dates are calculated — Naegele's rule
The standard method for calculating due dates — used by OBs worldwide — is Naegele's rule, developed in the 19th century. Despite its age, it remains the clinical standard because it works well for women with regular 28-day cycles.
- ·Naegele's rule: add 7 days to the first day of the last menstrual period, then add 9 months (or subtract 3 months)
- ·This assumes a 28-day cycle with ovulation on day 14 — if your cycle is shorter or longer, conception occurred earlier or later
- ·First trimester ultrasound (7–13 weeks) measures the fetal crown-rump length (CRL) and is more accurate than LMP dating
- ·If LMP dating and ultrasound dating differ by more than 5 days (first trimester) or 10 days (second trimester), ultrasound dating takes precedence
- ·IVF due dates are the most precise because the exact embryo transfer date is known
What "term" means for pregnancy timing
Not all births at full term are equal — research has led to more precise definitions of gestational maturity.
| Classification | Gestational age | Notes |
|---|---|---|
| Extremely preterm | < 28 weeks | Highest NICU risk; requires intensive care |
| Very preterm | 28–31 weeks | Significant NICU care typically needed |
| Moderate/late preterm | 32–36 weeks | Lungs often need support; shorter NICU stay |
| Early term | 37–38 weeks | Outcomes slightly better than preterm but less optimal than full term |
| Full term | 39–40 weeks | Optimal for fetal brain, lung, and organ development |
| Late term | 41 weeks | Increased monitoring; may discuss induction |
| Post-term | 42+ weeks | Induction typically recommended; increased complication risk |
First trimester prenatal care checklist
The first trimester (weeks 1–12) is when foundational prenatal care begins. Here's what to expect in early pregnancy:
- ·Confirm pregnancy with an OB or midwife — typically your first appointment is at 8–10 weeks
- ·Begin prenatal vitamins with folic acid (400–800 mcg/day) — ideally before conception
- ·First trimester ultrasound (7–13 weeks) — confirms viability, checks for twins, and gives an accurate due date
- ·NIPT (non-invasive prenatal testing) blood test — optional screening for chromosomal conditions; done at 10+ weeks
- ·Nuchal translucency ultrasound — screens for Down syndrome; done at 11–14 weeks
- ·Avoid: alcohol, high-mercury fish, raw/undercooked meat, unpasteurized dairy, and NSAIDs like ibuprofen
- ·Safe medications: acetaminophen (Tylenol) is generally considered safe; confirm all medications with your OB