Pregnancy Calculator
Calculate your pregnancy due date and track your baby's development week by week.
Understanding Your Pregnancy Timeline
Pregnancy typically lasts 40 weeks (280 days) from the first day of your last menstrual period. This is divided into three trimesters, each bringing unique developmental milestones and physical changes for both mother and baby.
How Due Dates Are Calculated
Healthcare providers use Naegele's Rule to calculate due dates: take the first day of your last menstrual period, add 7 days, subtract 3 months, and add 1 year. Our calculator automates this process and adjusts for cycle lengths different from the standard 28 days.
- Last Menstrual Period (LMP): The starting point for pregnancy dating
- Conception Date: Typically occurs 2 weeks after LMP during ovulation
- Gestational Age: Counted from LMP, not conception (about 2 weeks longer than fetal age)
- Due Date: LMP + 280 days (40 weeks), adjusted for cycle length
Pregnancy by Trimester
First Trimester (Weeks 1-13)
Mother: Morning sickness, fatigue, breast tenderness, frequent urination, mood changes
Baby: All major organs and body systems begin forming. Heart starts beating by week 6. By week 13, baby is fully formed but tiny (3 inches, 1 ounce).
Key Milestones: First prenatal visit (week 8-10), first ultrasound, possible genetic screening
Second Trimester (Weeks 14-27)
Mother: Energy returns, "pregnancy glow," baby bump grows, may feel baby movements (week 16-25)
Baby: Rapid growth period. Develops hearing, can hiccup, practices breathing movements. Gender may be visible on ultrasound (week 18-20). By week 27, weighs about 2 pounds.
Key Milestones: Anatomy scan (week 18-20), glucose screening (week 24-28), baby's movements become regular
Third Trimester (Weeks 28-40)
Mother: Braxton Hicks contractions, shortness of breath, back pain, frequent urination returns, difficulty sleeping
Baby: Final weight gain (gains half their birth weight in last 8 weeks). Brain develops rapidly. Lungs mature. Settles into head-down position. Full term at 37 weeks, average birth weight 6-9 pounds.
Key Milestones: Hospital tour, childbirth classes, weekly checkups from week 36, monitoring for labor signs
Fetal Development Highlights
| Week | Size Comparison | Major Developments |
|---|---|---|
| 4 | Poppy seed | Embryo implants, neural tube forms |
| 8 | Raspberry | Heart beating, webbed fingers and toes |
| 12 | Lime | Reflexes develop, kidneys produce urine |
| 16 | Avocado | Gender visible, eyes move, heart pumps 25 quarts/day |
| 20 | Banana | Hair grows, taste buds form, may suck thumb |
| 24 | Ear of corn | Lungs developing, footprints and fingerprints |
| 28 | Eggplant | Eyes open, can dream, responds to music |
| 32 | Squash | Practices breathing, gains ½ pound per week |
| 36 | Honeydew melon | Fully developed, preparing for birth |
| 40 | Small watermelon | Ready for birth! Average 7.5 pounds, 20 inches |
Important Prenatal Tests & Screenings
- First Prenatal Visit (8-10 weeks): Confirm pregnancy, blood tests, urine tests, medical history
- Nuchal Translucency Screening (11-13 weeks): Ultrasound for chromosomal abnormalities
- Cell-Free DNA Test (10+ weeks): Optional blood test for genetic conditions
- Anatomy Scan (18-20 weeks): Detailed ultrasound checking organs, growth, placenta position
- Glucose Screening (24-28 weeks): Test for gestational diabetes
- Group B Strep Test (35-37 weeks): Swab test to check for bacteria
Signs of Labor
Contact your healthcare provider if you experience:
- Regular contractions: 5 minutes apart, lasting 1 minute, for 1 hour (5-1-1 rule)
- Water breaking: Gush or trickle of clear or straw-colored fluid
- Bloody show: Mucus plug discharge with blood
- Severe pain: Constant abdominal pain or severe back pain
- Reduced movement: Less than 10 movements in 2 hours after 28 weeks
When to Call Your Doctor
Seek immediate medical attention if you experience:
- Severe abdominal pain or cramping
- Heavy vaginal bleeding (more than spotting)
- Severe headache, vision changes, or swelling (signs of preeclampsia)
- Fluid leaking from vagina before 37 weeks
- Fever over 100.4°F (38°C)
- Burning during urination
- Decreased fetal movement
Frequently Asked Questions
How accurate is a pregnancy due date calculator?
Due date calculators are estimates based on a 40-week pregnancy from your last menstrual period. Only about 5% of babies are born exactly on their due date. Most babies arrive within 2 weeks before or after. An ultrasound, especially in the first trimester, provides the most accurate due date.
When should I take a pregnancy test?
Take a home pregnancy test on the first day of your missed period for the most accurate result. Some sensitive tests can detect pregnancy 6-8 days after ovulation, but waiting until after your missed period reduces false negatives. If negative but still no period, test again in a few days.
What is the difference between gestational age and fetal age?
Gestational age is calculated from the first day of your last menstrual period and is about 2 weeks longer than fetal age. Fetal age (conceptional age) is calculated from conception, which typically occurs about 2 weeks after your LMP. Doctors typically use gestational age.
How are the three trimesters divided?
First trimester: Weeks 1-13 (major organ development). Second trimester: Weeks 14-27 (rapid growth, movement felt). Third trimester: Weeks 28-40 (final weight gain, lung maturation). Each trimester brings unique developmental milestones and physical changes.
Can my due date change?
Yes, especially if an early ultrasound shows the baby is measuring significantly larger or smaller than expected. First-trimester ultrasounds are most accurate for dating. Your doctor may adjust your due date if there's a discrepancy of more than 5-7 days from the LMP calculation.
What if my cycle is irregular?
If you have irregular cycles, calculating your due date from LMP alone may be less accurate. An early ultrasound (7-9 weeks) is the best way to establish your due date. You can also adjust the cycle length in our calculator if you know your average cycle length differs from 28 days.
What happens if I go past my due date?
Going 1-2 weeks past your due date is normal. Your doctor will monitor you more frequently after 40 weeks. Most providers will discuss induction between 41-42 weeks to reduce risks. About 50% of first-time mothers deliver after their due date.
How often should I see my doctor during pregnancy?
Typical prenatal visit schedule: Every 4 weeks until 28 weeks, every 2 weeks from 28-36 weeks, then weekly until delivery. High-risk pregnancies may require more frequent visits. First prenatal visit is usually at 8-10 weeks.
I nostri esperti hanno selezionato
Prodotti Consigliati
Aggiornato Febbraio 2026 · Testati e verificati
Digital Basal Body Thermometer
💡 Perché lo consigliamo
Accurate fertility tracking thermometer for pregnancy planning
Pregnancy Pillow with Support
Comfortable pregnancy support pillow for better sleep during pregnancy
🔗 Link affiliato Amazon — supporti CalcFast senza costi aggiuntivi
Prenatal Vitamins with Folic Acid
Essential vitamins for healthy pregnancy and fetal development
🔗 Link affiliato Amazon — supporti CalcFast senza costi aggiuntivi
🔗 Link affiliato Amazon — supporti CalcFast senza costi aggiuntivi