Pregnancy Due Date Calculator — Estimate Your Baby's Arrival
Calculate your estimated due date based on your last menstrual period or conception date. Understand how due dates are calculated and what to expect by trimester.
Finding out you're pregnant and immediately wanting to know when the baby arrives is one of the most universal moments in expecting parenthood. Your due date isn't just a countdown — it structures your prenatal care schedule, informs when to take certain tests, and helps your care team monitor growth milestones.
Use the pregnancy due date calculator on CalcHub to get your estimated date right now.
How Due Dates Are Calculated
The standard method is Naegele's Rule, developed in the 1800s and still in widespread clinical use:
Take the first day of your last menstrual period (LMP), add 7 days, then add 9 months (or subtract 3 months and add 1 year). That gives you the estimated due date.
It assumes a 28-day cycle with ovulation on day 14. For women with shorter or longer cycles, the estimate shifts accordingly — the CalcHub calculator lets you adjust for cycle length.
If you know your conception date (from IVF or tracking), that's even more accurate: add 266 days (38 weeks) to the conception date.
Pregnancy Timeline at a Glance
| Period | Weeks | Key Milestones |
|---|---|---|
| First trimester | Weeks 1–12 | Organ formation, first OB visit, optional genetic screening |
| Second trimester | Weeks 13–26 | Anatomy scan (~20 weeks), movement felt, gender reveal possible |
| Third trimester | Weeks 27–40 | Rapid growth, GBS test, birth plan preparation |
| Full term | Weeks 39–40 | Optimal delivery window |
| Post-term | 41+ weeks | Monitoring increases, possible induction discussed |
Why Your Due Date Will Probably Change
The LMP-based due date is a starting estimate. Your care provider will confirm (or adjust) it at your first ultrasound, usually done between 8–12 weeks. Early ultrasound measurements of the embryo's crown-rump length are the most accurate way to date a pregnancy.
Factors that can shift the estimate:
- Irregular menstrual cycles
- Recent hormonal contraception use
- Conceived while breastfeeding
- Polycystic ovary syndrome (PCOS) affecting ovulation timing
Don't be surprised if your "official" due date shifts by a week or two after your first scan — that's completely normal.
Only About 5% of Babies Arrive on Their Due Date
The due date is the midpoint of a normal delivery window, not a deadline. About 80% of babies arrive within two weeks on either side of the due date. First-time mothers tend to go slightly past their due date on average.
This calculator provides an estimate only. Accurate dating requires ultrasound confirmation. Always follow the guidance of your obstetrician or midwife for prenatal care decisions.Can I calculate my due date if I have irregular periods?
Yes, but with lower accuracy from the LMP method alone. If your cycles are significantly longer or shorter than 28 days, input your average cycle length into the calculator for a better estimate. Your first-trimester ultrasound will give the most reliable date regardless of cycle regularity.
What does "gestational age" mean vs. how old the baby actually is?
Gestational age counts from the first day of your LMP, which is typically about 2 weeks before conception. So when your care provider says "you're 8 weeks pregnant," the embryo is actually about 6 weeks old. This is standard clinical practice worldwide — gestational age is always measured from LMP.
Is a due date the same as the date I should give birth?
Not quite. It's an estimate of when 40 weeks of pregnancy will be complete. Most providers monitor closely after 40 weeks and may discuss induction around 41–42 weeks. The decision depends on your health, the baby's wellbeing, and clinical judgment — your care team will guide you.
Related Calculators
- BMI Calculator — track your BMI before and during pregnancy
- Water Intake Calculator — hydration needs increase significantly during pregnancy
- Calorie Calculator — calorie needs by trimester