Pregnancy Calculator
Written by The Kalcule Team
Calculate your due date and track important pregnancy milestones with our pregnancy calculator. Get personalized insights based on your last menstrual period and cycle length.
Why Due Date Calculation Matters
Knowing your estimated due date helps you prepare for your baby's arrival and track important prenatal development milestones. It also helps healthcare providers monitor your pregnancy progress and plan appropriate care.
How to Use the Pregnancy Calculator
- 1Select the first day of your last menstrual period
- 2Choose your average cycle length
- 3Get your estimated due date and pregnancy timeline
- 4View your current trimester and important milestones
Tips for a Healthy Pregnancy
Start prenatal care early, take recommended vitamins, maintain a healthy diet, and stay active as approved by your healthcare provider. Keep track of your appointments and important pregnancy milestones.
Calculate your baby's delivery date based on
The first day of your last menstrual cycle
September 2026
Frequently Asked Questions
Find answers to common questions about pregnancy due dates, gestational age calculation, and pregnancy milestones. Learn about different calculation methods, accuracy factors, and important prenatal dates.
The calculator provides an estimate based on Naegele's rule, a standard method used by healthcare providers. Only about 5% of babies are born on their exact due date, with most arriving within two weeks before or after.
If you're unsure about your last period date, consult your healthcare provider. They can determine gestational age through ultrasound and other clinical assessments.
The common form adds 280 days (40 weeks) to the first day of the last menstrual period, which assumes a 28-day cycle with ovulation around day 14. ACOG and others treat ultrasound dating as more accurate when it is available, especially early in pregnancy.
Clinics often adjust for cycle length and rely on first-trimester ultrasound. This calculator uses a simple rule. The clinic date is the one to follow for care.
A longer follicular phase usually means ovulation was later, so a period-based due date can be too early. Tell your clinician your typical cycle length; they may adjust dating.
Gestational age is conventionally counted from the last period, about two weeks before conception in a textbook cycle. If you know conception date (for example IVF), your clinic will date the pregnancy from that protocol, not from this page.
Only about 5% of births happen on the estimated due date. It is a midpoint for planning, not an appointment with the baby. Full term is a range of weeks, not a single day.
A period-based estimate is unreliable when cycles vary widely. Early ultrasound is the standard way to date those pregnancies. See a clinician rather than trusting this form.
No. Prenatal vitamins, screening, and appointment schedules come from your obstetric provider. Use this only to understand the arithmetic behind a common dating rule.
Gestational age starts from the last menstrual period. Fetal (conceptual) age is about two weeks shorter in a typical cycle. Medicine almost always speaks in gestational weeks.
Still have questions?
If you couldn't find the answer you were looking for, please contact our support team for personalized assistance.
Prepare for Your Journey
Use this calculator as a starting point in your pregnancy journey. Remember to attend all prenatal appointments and discuss any concerns with your healthcare provider.
Naegele’s rule in context
Adding 280 days to the first day of the last menstrual period is a nineteenth-century rule of thumb that still appears in textbooks. It assumes a 28-day cycle. ACOG and most clinics prefer early ultrasound when dates matter for screening windows.
A due date is a statistical midpoint. Most births occur across a range of weeks around it. Use your obstetric provider’s dating for care; use this calculator to see the arithmetic.
When the calendar is the wrong tool
Irregular cycles, uncertain last-period dates, lactation amenorrhoea and assisted reproduction all break the simple rule. Those pregnancies are dated with clinic protocols, not a public form.
How this calculator should be used
Use it to see Naegele arithmetic and a midpoint due date. Use your obstetric provider for screening windows, induction decisions and anything that changes care. Pair it with the ovulation calculator only as a prior — not as contraception or a diagnosis. See what this site will not claim.
What a due date is not
It is not a guarantee of the birth day, a substitute for dating ultrasound, or a reason to ignore bleeding, pain or reduced movements. If those happen, seek urgent care. This page cites ACOG-facing public material for fetal growth context; it is not an ACOG clinical opinion on your pregnancy.
Formula source: Naegele's rule — American College of Obstetricians and Gynecologists