Pregnancy Calculator
Calculate pregnancy milestones and due date
Pregnancy Details
Pro Tip
This calculator provides estimates. Ultrasound measurements provide more accurate due dates!
Privacy & Security
Your pregnancy information is completely private and secure. All calculations are performed locally in your browser - no personal pregnancy data is transmitted or stored. Your information remains confidential.
What is a Pregnancy Calculator?
A pregnancy calculator is a comprehensive prenatal tool that helps expectant parents track pregnancy progress by calculating gestational age, due date, conception date, current trimester, and important developmental milestones throughout the pregnancy journey. Understanding where you are in pregnancy is essential for proper prenatal care, monitoring fetal development, scheduling appropriate medical tests and screenings, preparing for childbirth, and managing the emotional journey of expecting a baby. Pregnancy is typically calculated from the first day of the last menstrual period (LMP), not from conception, because most women know their period date but not the exact conception date. This method results in a 40-week (280-day) pregnancy counting from LMP, though actual time from conception to birth is about 38 weeks since conception typically occurs about 2 weeks after the period starts. The calculator uses your LMP to determine your current gestational age in weeks and days, calculate your estimated due date (EDD) which is 40 weeks from LMP, identify which trimester you're currently in, estimate when conception likely occurred, and project important milestones like when baby's heartbeat becomes detectable, when you might feel first movements, and when various prenatal tests typically occur. Pregnancy is divided into three trimesters: First trimester (weeks 1-12) involves rapid initial development with major organs forming, heightened pregnancy symptoms, and highest miscarriage risk; Second trimester (weeks 13-26) is often called the "honeymoon period" with reduced symptoms, visible baby bump, feeling baby movements, and anatomy scans; Third trimester (weeks 27-40) features rapid growth, final organ maturation, preparation for birth, and increasing physical discomfort. Understanding your gestational age ensures you receive appropriate prenatal care at the right times, helps you track normal fetal development and identify potential concerns early, allows you to prepare appropriately for each pregnancy stage, connects you to relevant information and resources for your specific week, and helps plan for maternity leave, nursery preparation, and other practical matters. Whether you've just discovered you're pregnant and want to know your due date, you're tracking your pregnancy week-by-week, you're unsure of your LMP and need to estimate conception date, or you want to understand what to expect at each stage, this calculator provides the essential pregnancy timeline information every expectant parent needs.
Key Features
Gestational Age Calculation
Determine exactly how many weeks and days pregnant you are
Due Date Estimation
Calculate your estimated due date (EDD) 40 weeks from last menstrual period
Trimester Identification
Know which trimester you're currently in and when the next begins
Conception Date Estimation
Estimate when conception likely occurred based on your LMP
Milestone Tracking
View important developmental milestones and when they occur
Prenatal Test Schedule
See when common prenatal tests and ultrasounds typically happen
Daily Countdown
Track days until your due date with a pregnancy countdown
Multiple Input Methods
Calculate from LMP, conception date, or ultrasound-confirmed due date
How to Use the Pregnancy Calculator
Enter Last Menstrual Period
Input the first day of your last menstrual period (LMP). This is the most common method for calculating pregnancy and what most healthcare providers use. Be as accurate as possible with the date.
Alternative: Enter Conception Date
If you know your conception date (from fertility treatments or tracking ovulation), you can enter that instead. The calculator will work backwards to determine your pregnancy timeline.
Alternative: Enter Known Due Date
If your due date was confirmed by early ultrasound (most accurate between 8-13 weeks), you can enter that date instead. Ultrasound dating can be more precise than LMP dating.
Review Your Gestational Age
See how many weeks and days pregnant you are. Pregnancy is measured in weeks (like 14 weeks 3 days) because fetal development progresses rapidly and weekly milestones matter.
Check Your Trimester and Milestones
View your current trimester, upcoming pregnancy milestones, when prenatal tests typically occur, and your estimated due date. Remember that only about 5% of babies arrive exactly on their due date.
Pregnancy Tracking Tips
- Document Your LMP: When trying to conceive or if pregnancy is possible, note the first day of each period in a calendar or app to ensure accurate dating if you become pregnant.
- Schedule Early Prenatal Care: Contact your healthcare provider as soon as you have a positive pregnancy test to schedule your first prenatal appointment and establish care.
- Remember Due Date Is an Estimate: Only 5% of babies arrive on their due date. Think of it as a target within a 4-week window (38-42 weeks) rather than an exact prediction.
- Track Pregnancy Milestones: Use pregnancy apps or journals to track weekly development, symptoms, and milestones throughout your pregnancy journey.
- Don't Compare Too Much: Every pregnancy is different. Your symptoms, when you show, when you feel movement, and when you deliver may differ from friends' experiences.
- Ask Questions During Appointments: Bring a list of questions to prenatal visits. Your healthcare provider is there to address your concerns and ensure you understand your pregnancy timeline.
Frequently Asked Questions
Why is pregnancy calculated from my last period, not conception?
Pregnancy is calculated from the first day of your last menstrual period (LMP) rather than from conception for practical and historical reasons, even though it seems counterintuitive since you're obviously not pregnant during your period. First, most women know when their last period started but don't know the exact day of conception, which typically occurs about 14 days after the period starts during ovulation. Sperm can survive 3-5 days in the female reproductive tract, so even if you know when intercourse occurred, the actual conception date might be several days later, making precise conception dating difficult. Second, this calculation method has been the medical standard for decades, allowing for consistent communication between healthcare providers, standardized prenatal care schedules, and reliable research comparing pregnancies. Third, early pregnancy ultrasounds measure fetal size to estimate gestational age, and these measurements are calibrated against the LMP-based dating system. Using LMP results in a 40-week (280-day) pregnancy from your period, even though conception occurs around week 2 and actual fetal age is about 2 weeks less than gestational age. This means during weeks 1-2 of your calculated pregnancy, you're not yet pregnant - you're in your menstrual period and approaching ovulation. It's admittedly confusing, but this system works because it uses a clear, identifiable date (first day of period) that most women remember. If you know your conception date from fertility treatments or precise ovulation tracking, you can calculate gestational age by adding 2 weeks to the time since conception. For example, if conception was 8 weeks ago, gestational age is 10 weeks. Healthcare providers may adjust your due date based on early ultrasound measurements if they differ significantly from LMP dating, as ultrasound dating in the first trimester is typically more accurate than LMP dating, especially if you have irregular cycles.
How accurate is my due date?
Your estimated due date (EDD) is a helpful guide but not a precise prediction - only about 5% of babies arrive exactly on their due date, while about 90% are born between 37-42 weeks. The due date represents the completion of 40 weeks from your LMP, but normal, healthy pregnancies can vary by several weeks. Several factors affect due date accuracy. First, calculation method matters: LMP-based dating assumes a 28-day cycle with ovulation on day 14, but many women have cycles ranging from 21-35 days with ovulation timing varying accordingly. If you have irregular cycles or don't remember your exact LMP, calculation is less accurate. Ultrasound dating, especially from early first trimester (8-13 weeks), is generally most accurate, with measurements accurate to within 3-5 days because fetal growth is very consistent at this stage. Later ultrasounds are less accurate for dating because individual growth variations increase. Second, natural biological variation means even with perfect dating, babies are ready to be born across a range of gestational ages. First-time mothers tend to deliver slightly later on average (40 weeks 3 days), while women who've had previous babies tend to deliver slightly earlier (39 weeks 5 days). Third, other factors influence when you'll go into labor: maternal age, body mass index, stress levels, physical activity, multiple pregnancies (twins, triplets), and genetic factors. Your healthcare provider considers your due date a target with a normal range being 37-42 weeks. Before 37 weeks is considered preterm, while past 42 weeks is post-term and typically prompts induction. Most providers discuss induction if you reach 41 weeks without labor starting. Rather than fixating on one date, think of your due date as the center of a roughly four-week window (38-42 weeks) when baby might arrive. This mindset reduces stress if your due date passes without labor starting, which happens in about 50% of first-time pregnancies.
What are the trimesters and what happens in each?
Pregnancy is divided into three trimesters of roughly 13 weeks each, with distinct fetal development, maternal changes, and prenatal care needs in each period. First Trimester (weeks 1-12) is characterized by rapid embryonic and fetal development with all major organs and systems forming by week 10, though the fetus is still very small (about 2 inches and 0.5 ounces by week 12). Maternal symptoms are often most intense during this period including morning sickness, extreme fatigue, frequent urination, breast tenderness, and food aversions, though some women experience minimal symptoms. Miscarriage risk is highest in the first trimester, with 80% of miscarriages occurring before week 12. Prenatal care includes confirming pregnancy, initial comprehensive exam, first ultrasound (around 8-12 weeks), prenatal screening tests, and addressing early pregnancy symptoms. Second Trimester (weeks 13-26) is often the easiest and most enjoyable period, often called the pregnancy 'honeymoon period.' Morning sickness typically subsides, energy returns, and risk of miscarriage decreases significantly. You'll start showing with a visible baby bump, feel baby's first movements (quickening) between 16-22 weeks, find out baby's sex during anatomy ultrasound (18-22 weeks), and may experience symptoms like back pain, leg cramps, or heartburn as baby grows. Fetal development includes rapid growth, development of hearing and response to sound, formation of fingerprints, and increasing activity. Prenatal care includes the detailed anatomy ultrasound, glucose screening for gestational diabetes (24-28 weeks), and regular check-ups. Third Trimester (weeks 27-40) involves final fetal development with rapid weight gain (baby gains about half their birth weight in the last 8 weeks), lung maturation, positioning for birth (usually head-down), and final brain development. Maternal symptoms often include increased discomfort from baby's size, Braxton Hicks contractions, pelvic pressure, frequent urination, trouble sleeping, swelling in feet and ankles, and increasing fatigue. You'll prepare for birth with childbirth classes, finalizing birth plans, and nesting behaviors. Prenatal care becomes more frequent (every 2 weeks from 28-36 weeks, then weekly until delivery), monitoring baby's position and growth, and discussing labor and delivery plans. Understanding these phases helps you know what to expect and ensures you're receiving appropriate care at each stage.
When will I start feeling the baby move?
Most women first feel fetal movement, called quickening, between 16-22 weeks of pregnancy, though the exact timing varies based on several factors. First-time mothers typically feel movement closer to 20 weeks because they're unfamiliar with the sensation and might not recognize it initially, often describing early movements as feeling like butterflies, gas bubbles, or gentle fluttering rather than obvious kicks. Women who've been pregnant before often recognize movements earlier, sometimes as early as 16 weeks, because they know what to expect and can distinguish baby movements from digestive sensations. Other factors affecting when you feel movement include placental position (anterior placentas located on the front uterine wall can cushion movements, delaying when you feel them), body weight (women with lower body fat percentages might feel movements earlier), and baby's activity level (some babies are naturally more active than others). The baby is actually moving much earlier than you can feel - movements start around 7-8 weeks, but the baby is too small and the movements too gentle to detect. As pregnancy progresses, movements become stronger and more obvious. By 24-28 weeks, movements should be regular and noticeable, and your provider might ask you to do kick counts starting around 28 weeks - monitoring that you feel a certain number of movements within a specific timeframe. Baby's activity patterns vary throughout the day, often becoming more active when you're resting or lying down, and less active when you're moving around. If you haven't felt movement by 22 weeks, contact your healthcare provider. They might perform an ultrasound to check on baby, though in most cases, everything is fine and movement just hasn't been strong enough to feel yet. After you start feeling regular movements, any significant decrease in movement or prolonged period without movement warrants contacting your provider, as movement is an important indicator of fetal wellbeing. The sensation of feeling your baby move is often one of the most exciting and reassuring parts of pregnancy, making the pregnancy feel more real and providing daily connection with your growing baby.
What prenatal tests and screenings happen at each stage?
Prenatal testing follows a general timeline designed to screen for potential problems and monitor healthy development at appropriate gestational ages. First Trimester (weeks 1-12) includes initial prenatal visit with comprehensive health history, physical exam, and blood tests checking blood type and Rh factor, complete blood count, immunity to rubella and chickenpox, sexually transmitted infections, and other health markers. First ultrasound around 8-12 weeks confirms pregnancy, dating, number of fetuses, and visible heartbeat. First-trimester screening (10-13 weeks) combines ultrasound measuring nuchal translucency (fluid at back of baby's neck) with blood tests for chromosomal abnormalities like Down syndrome. Cell-free fetal DNA screening (NIPT) can be done from 10 weeks onward, testing for chromosomal conditions through maternal blood sample. Second Trimester (weeks 13-26) features the detailed anatomy ultrasound (18-22 weeks), a comprehensive scan examining all organs, limbs, and structures to detect physical abnormalities, along with checking placenta position and amniotic fluid levels. This is often when parents learn baby's sex if they choose. Quad screen or multiple marker screening (15-20 weeks) is a blood test screening for neural tube defects and chromosomal abnormalities. Glucose screening (24-28 weeks) tests for gestational diabetes through a one-hour glucose challenge test, with additional testing if results are abnormal. Some women receive additional screening for anemia or other conditions. Third Trimester (weeks 27-40) includes Group B strep screening (35-37 weeks), a vaginal and rectal swab checking for bacteria that could be transmitted to baby during delivery, requiring antibiotics during labor if positive. Regular check-ups monitor baby's position, size, and heart rate, with increased frequency (every 2 weeks from 28-36 weeks, then weekly until delivery). Depending on circumstances, additional testing might include biophysical profile (ultrasound evaluating baby's wellbeing), non-stress test (monitoring baby's heart rate and movements), or growth ultrasounds if concerns about size exist. Some providers perform cervical checks in late pregnancy to assess labor readiness. Optional testing throughout pregnancy might include diagnostic tests like chorionic villus sampling (CVS) at 10-13 weeks or amniocentesis at 15-20 weeks if screening suggests potential problems, providing definitive chromosomal information but carrying small risk. The specific tests you receive depend on your age, health history, family history, pregnancy risk factors, and personal preferences. Discuss with your provider which tests are recommended for your situation and what results mean.
Is it normal if my due date changes after an ultrasound?
Yes, it's common and normal for healthcare providers to adjust your due date based on early ultrasound measurements, and this doesn't necessarily indicate a problem. Due dates can be adjusted for several legitimate reasons. First, early ultrasounds (especially 8-13 weeks) are more accurate for pregnancy dating than LMP-based calculations because fetal size is very consistent at early gestational ages, with measurements accurate to within 3-5 days. If early ultrasound dating differs from LMP dating by more than 5-7 days, most providers adjust to the ultrasound date. Second, LMP-based dating assumes regular 28-day cycles with ovulation on day 14, but many women have irregular cycles, longer or shorter cycles, or don't ovulate exactly mid-cycle. If your cycle varies from this standard, your LMP date won't accurately reflect conception timing. Third, you might have experienced light bleeding early in pregnancy that you mistook for a period, making your remembered LMP inaccurate. Fourth, if you conceived very quickly after stopping birth control or immediately postpartum, your cycles might not have returned to normal patterns yet. When providers adjust due dates, they use the ultrasound measurements because they reflect actual fetal development more accurately than calendar calculations. First-trimester ultrasounds measure crown-rump length (CRL), which corresponds very reliably to gestational age. If the measurement suggests you're 9 weeks along but LMP dating suggested 11 weeks, you likely ovulated later than assumed, so conception was more recent. Your due date would be adjusted forward accordingly. Conversely, if ultrasound shows more development than LMP dating suggested, your due date moves earlier. Later ultrasounds (second and third trimester) are not used for dating adjustments because individual growth variations increase, making size less reliable for determining gestational age. Changes of a few days to a week are normal and nothing to worry about. However, if there's a significant discrepancy (more than 2 weeks difference), your provider will investigate further to ensure accurate dating and healthy development. Once your due date is adjusted based on first-trimester ultrasound, it typically doesn't change again unless there's clear evidence of a dating error. Having your due date adjusted doesn't mean anything is wrong with your baby - it simply means your pregnancy timeline is being calibrated more accurately based on actual development rather than estimated conception timing.
What if I don't know my last menstrual period date?
If you don't know your last menstrual period (LMP) date, either because you have irregular periods, weren't tracking your cycles, recently stopped hormonal birth control, are breastfeeding, or simply don't remember, you can still determine your gestational age and due date through alternative methods. The most accurate method is early ultrasound dating, with first-trimester ultrasounds (especially 8-13 weeks) providing the most accurate dating, measuring crown-rump length to determine gestational age within 3-5 days accuracy. If you don't know your LMP, your healthcare provider will order a dating ultrasound as soon as possible to establish gestational age. The earlier this ultrasound is performed, the more accurate the dating will be. If you know or can estimate your conception date from fertility treatments, tracking ovulation, or knowing when you had intercourse, gestational age can be calculated by adding 2 weeks to the time since conception, since standard pregnancy dating includes the 2 weeks before conception. For example, if you conceived 6 weeks ago, you're about 8 weeks pregnant by gestational age. If you received a positive pregnancy test, the timing can provide clues. Most tests detect pregnancy 12-14 days after conception, so a positive test suggests you're at least 4-5 weeks gestational age (2 weeks from conception plus the 2 weeks before ovulation). Physical exam findings like uterine size and presence of fetal heartbeat (detectable by Doppler around 10-12 weeks, by ultrasound around 6 weeks) can estimate gestational age, though these are less precise than ultrasound measurements. Blood hCG levels can suggest approximate gestational age in very early pregnancy, though levels vary widely between women and overlap across gestational ages, making this method imprecise. For women with completely unknown dating and late presentation to prenatal care (after first trimester), second-trimester ultrasounds can estimate gestational age but with less accuracy (plus or minus 1-2 weeks) due to individual growth variations. Not knowing your LMP doesn't prevent proper prenatal care - early ultrasound dating is actually more accurate than LMP dating in many cases. Schedule prenatal care as soon as you know you're pregnant, and your provider will establish accurate dating through examination and ultrasound. Going forward, tracking your menstrual cycles (using apps, calendars, or fertility awareness methods) can be helpful not just for pregnancy dating but also for understanding your body and identifying potential health issues. However, don't let not knowing your LMP delay seeking prenatal care - accurate dating can be established through other means.
How does being pregnant with twins affect my due date?
Twin pregnancies have shorter gestation periods than singleton pregnancies, with different due date considerations and higher likelihood of early delivery. While singleton pregnancies are calculated at 40 weeks from LMP and typically deliver between 38-42 weeks, twin pregnancies naturally conclude earlier on average. Uncomplicated twin pregnancies typically deliver around 36-37 weeks, with many twins born between 35-38 weeks. Twins are considered full-term at 38 weeks (compared to 40 weeks for singletons), and many providers recommend delivery by 38-39 weeks even without complications due to increased risks of continuing the pregnancy beyond this point. Due date calculation for twins starts the same as singletons - 40 weeks from LMP or based on early ultrasound dating. However, your provider will likely discuss a different target delivery window. Many recommend not continuing twin pregnancies beyond 38-39 weeks, so your 'target' delivery date might be 37-38 weeks rather than 40 weeks, though your official EDD remains at 40 weeks for charting purposes. Factors affecting twin delivery timing include chorionicity (identical twins sharing a placenta are at higher risk and often delivered earlier, around 36 weeks; non-identical twins with separate placentas might go slightly later), presence of complications (preeclampsia, gestational diabetes, growth discordance, or other issues often require earlier delivery), baby positioning (whether they're both head-down affects delivery timing and method), and maternal factors including age, overall health, and previous pregnancy history. Even without complications, about 60% of twins are born before 37 weeks, with about 12% born before 32 weeks (very preterm). The increased early delivery rate occurs because carrying multiple babies creates more physical demand on the mother's body, increases risk of complications like preeclampsia and gestational diabetes, can cause premature labor due to uterine stretching, and involves higher risk of growth issues or placental problems. Your prenatal care for twins will be more frequent than for singletons, with ultrasounds every 4-6 weeks to monitor growth and development, more frequent appointments in the third trimester, increased monitoring for complications, and detailed discussions about delivery timing and method. Some twin pregnancies deliver vaginally, while others require cesarean section depending on positioning and circumstances. Understanding that twins naturally deliver earlier helps set appropriate expectations. Rather than thinking you'll make it to your 40-week due date, plan for delivery somewhere between 35-38 weeks for most twin pregnancies. This means preparing earlier - having the nursery ready, hospital bags packed, work transition planned, and support arranged by 32-34 weeks rather than 38-39 weeks. Despite earlier delivery, most twins born after 35 weeks do very well with minimal complications, though they might need short NICU stays for monitoring or feeding support.
Why Use Our Pregnancy Calculator?
Understanding your pregnancy timeline is essential for proper prenatal care, monitoring development, and preparing for your baby's arrival. Our pregnancy calculator provides accurate gestational age calculations, trimester identification, and milestone tracking based on your last menstrual period or other known dates. Whether you just discovered you're pregnant and want to know your due date, you're tracking your pregnancy week by week, or you want to understand what developmental stages and prenatal care to expect, this calculator gives you the essential timeline information every expectant parent needs. Remember that every pregnancy is unique, and our calculator provides estimates to guide discussions with your healthcare provider.