Enter the first day of your last menstrual period and your cycle length (typically 28 days). The calculator instantly estimates your due date, current gestational age in weeks and days, the trimester you’re in, days remaining until delivery, and both the conception and trimester end dates.
Free pregnancy due date calculator – no sign‑up
Calculate Your Pregnancy Due Date in Seconds
Enter the first day of your last menstrual period (LMP) and your cycle length to instantly see your estimated due date, conception window, current week, and trimester. Follow your baby’s journey with a personalized timeline — all free, private, and instant.
Start Your Pregnancy Journey with Confidence
Finding out you’re pregnant is an exciting, life‑changing moment — and one of the first questions you’ll have is, “When am I due?” Our Pregnancy Calculator uses the standard Naegele’s Rule, based on your last menstrual period (LMP) and cycle length, to give you an accurate estimated due date. You’ll also instantly see your conception window, how many weeks pregnant you are, which trimester you’re in, and key milestones like the end of each trimester and the first heartbeat. It’s fast, private, and completely free.
What Is a Pregnancy Calculator?
A pregnancy calculator (also called a due date calculator) is a free online tool that estimates your baby’s birth date based on the first day of your last menstrual period (LMP) and the typical length of your menstrual cycle. Most calculators use Naegele’s Rule: add 280 days (40 weeks) to the first day of your LMP, then adjust for your actual cycle length. The tool also provides your current gestational age (in weeks and days), your conception window, and the trimester you’re in. It’s an essential first step for expectant parents, helping you plan appointments, prepare for maternity leave, and follow your baby’s development.
How to Use the Pregnancy Calculator
Enter the First Day of Your Last Period
Use the date picker to select the first day of your last menstrual period. This is the most important input.
Add Your Cycle Length (Optional)
The default is 28 days. If your cycle is usually longer or shorter, enter that for a more accurate due date.
View Your Pregnancy Timeline
Instantly see your estimated due date, conception window, current week and day, trimester, and important future milestones — no sign‑up required.
How the Pregnancy Calculator Determines Your Dates
The calculator uses Naegele’s Rule, the standard method used by obstetricians. It takes the first day of your last menstrual period (LMP), adds 280 days (40 weeks), and then adjusts for your cycle length: if your cycle is 30 days, it adds an extra 2 days; if it’s 26 days, it subtracts 2 days. The conception window is estimated as the day of ovulation, typically 14 days before the next expected period. Current gestational age is calculated from LMP to today, divided into weeks and days. The trimester is determined by the week: first trimester (weeks 1–13), second (weeks 14–27), and third (weeks 28–40). All calculations run locally in your browser for complete privacy.
Naegele’s Rule
Due Date = LMP + 280 days + (Cycle Length – 28)
Conception ≈ LMP + (Cycle Length – 14) days. Current week = (Today – LMP) / 7.
Key Features of This Pregnancy Calculator
Instant Due Date Estimate
Based on your LMP and cycle length, get an accurate due date within seconds.
Personalized Timeline
See your conception window, current week and day, trimester, and how many days remain.
Trimester and Milestones
Instantly know which trimester you’re in and when the next one begins, plus key fetal development dates.
Private & Secure
Your dates and cycle details remain on your device. Nothing is ever uploaded or shared.
Benefits of Using a Due Date Calculator
- ✅ Plan prenatal care – schedule first appointments and screenings based on your estimated gestation
- ✅ Prepare for maternity leave – give your employer a clear estimated departure date
- ✅ Track baby’s growth – follow week‑by‑week development guides aligned with your due date
- ✅ Share with loved ones – announce your due date with confidence
- ✅ Peace of mind – replace guesswork with a medically recognized calculation
Understanding Pregnancy Trimesters
First Trimester (Weeks 1‑13)
The most critical developmental period. Organs form, and the heart begins to beat. Fatigue and morning sickness are common.
Second Trimester (Weeks 14‑27)
Often called the “golden period.” Energy returns, and the baby’s movements become noticeable. The anatomy scan typically occurs around week 20.
Third Trimester (Weeks 28‑40)
Rapid growth and final preparations for birth. Monitoring increases, and labor can begin anytime from week 37 onward.
How Accurate Is the Due Date Calculation?
Naegele’s Rule is accurate for about 80% of women, assuming a regular 28‑day cycle. However, only about 4% of babies are born exactly on their due date. Most arrive within a week before or after. Your healthcare provider may adjust the date after an early ultrasound, which is the most accurate method. Use the calculator as a reliable starting point and discuss the final due date with your doctor.
Conception Window and Fertility
Estimated Conception Date
Ovulation typically occurs around day 14 of a 28‑day cycle. The calculator estimates conception based on your LMP and cycle length.
Fertile Window
Sperm can survive up to 5 days, so the fertile window includes the days leading up to ovulation. The calculator shows the likely conception range.
Key Milestones in Fetal Development
Around 6 weeks, a heartbeat can often be detected via ultrasound. By 12 weeks, most major organs are formed. At 20 weeks, the anatomy scan gives a detailed look at the baby. By 28 weeks, the baby can open its eyes and respond to sound. The calculator shows these milestones relative to your due date, giving you a personalized guide to your baby’s growth.
Example Due Date Calculation
Sara’s last menstrual period started on January 10, 2025. She has a typical 28‑day cycle. Using Naegele’s Rule, the estimated due date is January 10 + 280 days = October 17, 2025. Her conception window would be around January 24, 2025. As of today, the calculator determines she is 18 weeks and 3 days pregnant, in her second trimester. The due date is 22 weeks away. The calculator provides all these details at a glance.
How to Prepare for Your Due Date
Once you have your due date, use it to book prenatal visits, schedule ultrasounds, plan your maternity leave, and prepare your home. Many parents also use it to announce the pregnancy and set up a baby registry. The calculator’s timeline helps you stay organized throughout the journey.
Factors That Affect Due Date Accuracy
- 📅 Cycle regularity and length
- 📏 Early ultrasound measurements
- 🧬 Genetics and family history
- 🤰 Multiple pregnancy (twins, etc.)
- 📈 Maternal age and health
- 💊 Fertility treatments and IVF
- 🩺 Medical conditions affecting pregnancy
- 📋 LMP recall accuracy
Detailed Pregnancy Timeline Scenario
Scenario: LMP March 15, 2025. Cycle length 30 days.
- ✅ Due Date: March 15 + 280 + (30‑28) = December 22, 2025
- ✅ Conception window: March 27‑31, 2025
- ✅ End of first trimester: June 15, 2025
- ✅ End of second trimester: September 20, 2025
- ✅ Today’s gestational age is calculated live — the tool updates every visit.
Who Can Use This Pregnancy Calculator?
- 🤰 Expectant mothers – get your first due date estimate at home
- 👩⚕️ Midwives & doulas – quickly calculate due dates for clients
- 📋 Fertility clinics – provide patients with an easy‑to‑use tool
- 👪 Partners & family – follow along with the pregnancy milestones
- 🎓 Health educators – teach reproductive health concepts
Key Pregnancy Terms
- Gestational Age
- The age of the pregnancy measured from the first day of the last menstrual period (LMP), in weeks and days.
- Naegele’s Rule
- A standard formula for estimating the due date: LMP + 280 days, adjusted for cycle length.
- Conception Window
- The estimated range of days when fertilization likely occurred, based on ovulation.
- Trimester
- One of three 13‑ to 14‑week periods that divide a pregnancy, each with distinct developmental milestones.
Tips for a Healthy Pregnancy Journey
- Schedule your first prenatal appointment soon after a positive pregnancy test.
- Begin taking a prenatal vitamin with folic acid if you haven’t already.
- Use the calculator’s milestones to prepare for important scans and tests.
- Keep a journal of your symptoms and questions to discuss with your provider.
- Remember that only about 4% of babies arrive on their due date — be flexible!
Advantages of This Pregnancy Calculator
- ✅ 100% free – no sign‑up, no ads
- ✅ Instant due date, conception window, and trimester detection
- ✅ Personalizes for cycle length for greater accuracy
- ✅ Visual timeline with milestones for your exact pregnancy stage
- ✅ Works on any device
- ✅ Private – your dates never leave your device
Limitations of Due Date Calculations
This calculator provides an estimate based on Naegele’s Rule. It does not replace an ultrasound‑confirmed due date, which is more accurate, especially in early pregnancy. It assumes a regular menstrual cycle and may be less accurate for those with irregular cycles, those using fertility treatments, or pregnancies conceived shortly after stopping hormonal birth control. Always consult your healthcare provider for your official due date.
Accuracy of Results
Naegele’s Rule is the standard obstetric method and is correct for the majority of women with regular cycles. However, the actual delivery date can vary. The calculator’s math is precise; individual biology adds the variability.
Security and Privacy
All calculations are performed locally in your browser. No menstrual dates or personal information is ever transmitted, stored, or shared. You can use the tool offline after the page loads.
Mobile‑Friendly Design
The pregnancy calculator is fully responsive. Use it on your smartphone, tablet, or desktop — all inputs, timelines, and results adapt seamlessly to any screen size.
Frequently Asked Questions
How is the due date calculated?
The most common method is Naegele’s Rule: start with the first day of your last menstrual period (LMP), add 280 days (40 weeks), and adjust for your usual cycle length. This calculator applies that exact formula.
What if I don’t know my LMP or have irregular cycles?
The calculator works best with a known LMP and regular cycle. If your cycles are irregular or you’re unsure of your LMP, an early ultrasound is the most accurate way to determine your due date.
How accurate is the due date?
For women with regular cycles, the estimate is usually within a week of the actual delivery date. Only about 4% of babies are born exactly on their due date, but it provides a reliable timeframe for planning.
Can I use this if I conceived through IVF?
IVF due dates are typically calculated from the embryo transfer date. This calculator is designed for natural conception. For IVF, use the date provided by your fertility clinic.
Does the calculator show the baby’s size or weight?
This tool focuses on dates and milestones. For week‑by‑week fetal development information, pair it with a pregnancy tracking app or your provider’s resources.
Is my personal data safe?
Absolutely. All calculations are local. No information is ever sent to a server or stored.
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Conclusion: Your Journey Begins with One Date
Pregnancy is a beautiful, transformative experience — and it helps to have a roadmap. This calculator gives you that first piece of the puzzle: your due date. Enter your information now and start counting down to the day you’ll meet your little one.
Ready to Calculate Your Due Date?
Enter the first day of your last period now – free, private, and instant.