First Trimester
Weeks 1 – 13
Major organs and body systems begin forming. Morning sickness, fatigue, and breast tenderness are common. First prenatal visit and early genetic screening (NIPT) happen during this stage.
Free Pregnancy Tool
Pregnancy Due Date Calculator
Find your estimated due date (EDD), current trimester, and key pregnancy milestones — based on your last period, conception date, or IVF transfer.
Uses Naegele's Rule: adds 280 days to your last period start date, adjusted for your cycle length.
If you know when you ovulated, your due date is approximately 266 days (38 weeks) from that date.
Due date = 266 days from fertilization, minus the embryo's age at transfer.
Enter the gestational age your doctor measured. First-trimester ultrasound is the most accurate dating method.
Your estimated due date
—
Shop for your trimester
⚠️ This is an estimate only. Only ~5% of babies arrive on their exact due date. Always confirm with your healthcare provider.
Curious how far along you are?See your exact pregnancy week, trimester, and how big your baby is right now.
Open Week Calculator →Your pregnancy journey by trimester
Second Trimester
Weeks 14 – 27
Often called the "honeymoon" trimester — most symptoms ease. You'll feel the first kicks (quickening) around weeks 18–22. Anatomy scan and gender reveal usually happen at week 20.
Third Trimester
Weeks 28 – 40+
Baby gains weight rapidly and moves into birth position. You may feel Braxton Hicks contractions and back pain. Group B strep test and birth planning begin around week 35–36.
Everything you need to know
How is a due date calculated?
Most due dates use Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. Cycle length adjustments shift the ovulation date accordingly.
When should I see a doctor?
Book your first prenatal appointment as soon as you get a positive pregnancy test — ideally before 8 weeks. Your OB or midwife will use an early ultrasound to confirm gestational age, which is the most accurate dating method available.
How accurate is this calculator?
Due date calculators provide estimates only. Only about 5% of babies are born on their exact EDD. Most arrive within 2 weeks either side. Factors like irregular cycles and late ovulation can shift the date.
What if I have irregular periods?
Use the conception date or ultrasound method instead. An early first-trimester ultrasound (7–12 weeks) is the gold standard for dating a pregnancy when LMP is uncertain or irregular. Tell your provider about irregular cycles.
Frequently asked questions
What is gestational age vs. fetal age?
Gestational age is counted from the first day of your last menstrual period, so technically you're "pregnant" for two weeks before conception. Fetal age (embryonic age) is counted from fertilization — about two weeks less than gestational age. Doctors almost always use gestational age.
Can my due date change after an ultrasound?
Yes. If your dating ultrasound shows a significant difference from the LMP-based date — usually more than 5–7 days in the first trimester — your provider may adjust (redate) your due date based on ultrasound measurements. This is completely normal.
What is a "full-term" pregnancy?
ACOG defines full-term as 39 weeks 0 days through 40 weeks 6 days. Early term is 37–38 weeks; late-term is 41–41+6 weeks. Babies born before 37 weeks are considered preterm. Most providers prefer to wait until at least 39 weeks for planned deliveries.
How are twins' due dates calculated?
The same Naegele's Rule applies, but twin pregnancies rarely reach 40 weeks. Uncomplicated fraternal twins are typically delivered around 38 weeks; monochorionic twins may be earlier. Your provider will discuss the timing specific to your pregnancy type.
When should I start shopping for maternity clothes?
Most people begin showing between 12–16 weeks (early second trimester). Waistbands often get uncomfortable around 10–12 weeks — maternity tops and leggings are great early picks. Full maternity jeans and dresses become essential by the second trimester. For special occasions, browse our photoshoot gowns and baby shower dresses.
What prenatal appointments should I expect?
Typically: first visit at 8–10 weeks (confirmation ultrasound), 12-week NIPT/nuchal scan, 20-week anatomy scan, monthly visits through 28 weeks, bi-weekly until 36 weeks, then weekly until delivery. Your provider may schedule more or fewer based on your risk factors.
